diff --git a/compose/cli/command.py b/compose/cli/command.py
index 67176df2..950cb166 100644
--- a/compose/cli/command.py
+++ b/compose/cli/command.py
@@ -51,57 +51,68 @@ class Command(DocoptCommand):
             handler(None, command_options)
             return
 
-        if 'FIG_FILE' in os.environ:
-            log.warn('The FIG_FILE environment variable is deprecated.')
-            log.warn('Please use COMPOSE_FILE instead.')
-
-        explicit_config_path = options.get('--file') or os.environ.get('COMPOSE_FILE') or os.environ.get('FIG_FILE')
-        project = self.get_project(
-            explicit_config_path,
+        project = get_project(
+            self.base_dir,
+            get_config_path(options.get('--file')),
             project_name=options.get('--project-name'),
             verbose=options.get('--verbose'))
 
         handler(project, command_options)
 
-    def get_client(self, verbose=False):
-        client = docker_client()
-        if verbose:
-            version_info = six.iteritems(client.version())
-            log.info("Compose version %s", __version__)
-            log.info("Docker base_url: %s", client.base_url)
-            log.info("Docker version: %s",
-                     ", ".join("%s=%s" % item for item in version_info))
-            return verbose_proxy.VerboseProxy('docker', client)
-        return client
 
-    def get_project(self, config_path=None, project_name=None, verbose=False):
-        config_details = config.find(self.base_dir, config_path)
+def get_config_path(file_option):
+    if file_option:
+        return file_option
 
-        try:
-            return Project.from_dicts(
-                self.get_project_name(config_details.working_dir, project_name),
-                config.load(config_details),
-                self.get_client(verbose=verbose))
-        except ConfigError as e:
-            raise errors.UserError(six.text_type(e))
+    if 'FIG_FILE' in os.environ:
+        log.warn('The FIG_FILE environment variable is deprecated.')
+        log.warn('Please use COMPOSE_FILE instead.')
 
-    def get_project_name(self, working_dir, project_name=None):
-        def normalize_name(name):
-            return re.sub(r'[^a-z0-9]', '', name.lower())
+    config_file = os.environ.get('COMPOSE_FILE') or os.environ.get('FIG_FILE')
+    return [config_file] if config_file else None
 
-        if 'FIG_PROJECT_NAME' in os.environ:
-            log.warn('The FIG_PROJECT_NAME environment variable is deprecated.')
-            log.warn('Please use COMPOSE_PROJECT_NAME instead.')
 
-        project_name = (
-            project_name or
-            os.environ.get('COMPOSE_PROJECT_NAME') or
-            os.environ.get('FIG_PROJECT_NAME'))
-        if project_name is not None:
-            return normalize_name(project_name)
+def get_client(verbose=False):
+    client = docker_client()
+    if verbose:
+        version_info = six.iteritems(client.version())
+        log.info("Compose version %s", __version__)
+        log.info("Docker base_url: %s", client.base_url)
+        log.info("Docker version: %s",
+                 ", ".join("%s=%s" % item for item in version_info))
+        return verbose_proxy.VerboseProxy('docker', client)
+    return client
 
-        project = os.path.basename(os.path.abspath(working_dir))
-        if project:
-            return normalize_name(project)
 
-        return 'default'
+def get_project(base_dir, config_path=None, project_name=None, verbose=False):
+    config_details = config.find(base_dir, config_path)
+
+    try:
+        return Project.from_dicts(
+            get_project_name(config_details.working_dir, project_name),
+            config.load(config_details),
+            get_client(verbose=verbose))
+    except ConfigError as e:
+        raise errors.UserError(six.text_type(e))
+
+
+def get_project_name(working_dir, project_name=None):
+    def normalize_name(name):
+        return re.sub(r'[^a-z0-9]', '', name.lower())
+
+    if 'FIG_PROJECT_NAME' in os.environ:
+        log.warn('The FIG_PROJECT_NAME environment variable is deprecated.')
+        log.warn('Please use COMPOSE_PROJECT_NAME instead.')
+
+    project_name = (
+        project_name or
+        os.environ.get('COMPOSE_PROJECT_NAME') or
+        os.environ.get('FIG_PROJECT_NAME'))
+    if project_name is not None:
+        return normalize_name(project_name)
+
+    project = os.path.basename(os.path.abspath(working_dir))
+    if project:
+        return normalize_name(project)
+
+    return 'default'
diff --git a/compose/cli/main.py b/compose/cli/main.py
index 9b03ea67..5f44f1cc 100644
--- a/compose/cli/main.py
+++ b/compose/cli/main.py
@@ -96,7 +96,7 @@ class TopLevelCommand(Command):
     """Define and run multi-container applications with Docker.
 
     Usage:
-      docker-compose [options] [COMMAND] [ARGS...]
+      docker-compose [-f=<arg>...] [options] [COMMAND] [ARGS...]
       docker-compose -h|--help
 
     Options:
diff --git a/compose/cli/utils.py b/compose/cli/utils.py
index 0b7ac683..0a4416c0 100644
--- a/compose/cli/utils.py
+++ b/compose/cli/utils.py
@@ -36,25 +36,6 @@ def yesno(prompt, default=None):
         return None
 
 
-def find_candidates_in_parent_dirs(filenames, path):
-    """
-    Given a directory path to start, looks for filenames in the
-    directory, and then each parent directory successively,
-    until found.
-
-    Returns tuple (candidates, path).
-    """
-    candidates = [filename for filename in filenames
-                  if os.path.exists(os.path.join(path, filename))]
-
-    if len(candidates) == 0:
-        parent_dir = os.path.join(path, '..')
-        if os.path.abspath(parent_dir) != os.path.abspath(path):
-            return find_candidates_in_parent_dirs(filenames, parent_dir)
-
-    return (candidates, path)
-
-
 def split_buffer(reader, separator):
     """
     Given a generator which yields strings and a separator string,
diff --git a/compose/config/config.py b/compose/config/config.py
index 840a28a1..94c5ab95 100644
--- a/compose/config/config.py
+++ b/compose/config/config.py
@@ -16,7 +16,6 @@ from .validation import validate_extended_service_exists
 from .validation import validate_extends_file_path
 from .validation import validate_service_names
 from .validation import validate_top_level_object
-from compose.cli.utils import find_candidates_in_parent_dirs
 
 
 DOCKER_CONFIG_KEYS = [
@@ -77,6 +76,7 @@ SUPPORTED_FILENAMES = [
     'fig.yaml',
 ]
 
+DEFAULT_OVERRIDE_FILENAME = 'docker-compose.override.yml'
 
 PATH_START_CHARS = [
     '/',
@@ -88,24 +88,45 @@ PATH_START_CHARS = [
 log = logging.getLogger(__name__)
 
 
-ConfigDetails = namedtuple('ConfigDetails', 'config working_dir filename')
+class ConfigDetails(namedtuple('_ConfigDetails', 'working_dir config_files')):
+    """
+    :param working_dir: the directory to use for relative paths in the config
+    :type  working_dir: string
+    :param config_files: list of configuration files to load
+    :type  config_files: list of :class:`ConfigFile`
+     """
 
 
-def find(base_dir, filename):
-    if filename == '-':
-        return ConfigDetails(yaml.safe_load(sys.stdin), os.getcwd(), None)
+class ConfigFile(namedtuple('_ConfigFile', 'filename config')):
+    """
+    :param filename: filename of the config file
+    :type  filename: string
+    :param config: contents of the config file
+    :type  config: :class:`dict`
+    """
 
-    if filename:
-        filename = os.path.join(base_dir, filename)
+
+def find(base_dir, filenames):
+    if filenames == ['-']:
+        return ConfigDetails(
+            os.getcwd(),
+            [ConfigFile(None, yaml.safe_load(sys.stdin))])
+
+    if filenames:
+        filenames = [os.path.join(base_dir, f) for f in filenames]
     else:
-        filename = get_config_path(base_dir)
-    return ConfigDetails(load_yaml(filename), os.path.dirname(filename), filename)
+        filenames = get_default_config_files(base_dir)
+
+    log.debug("Using configuration files: {}".format(",".join(filenames)))
+    return ConfigDetails(
+        os.path.dirname(filenames[0]),
+        [ConfigFile(f, load_yaml(f)) for f in filenames])
 
 
-def get_config_path(base_dir):
+def get_default_config_files(base_dir):
     (candidates, path) = find_candidates_in_parent_dirs(SUPPORTED_FILENAMES, base_dir)
 
-    if len(candidates) == 0:
+    if not candidates:
         raise ComposeFileNotFound(SUPPORTED_FILENAMES)
 
     winner = candidates[0]
@@ -123,7 +144,31 @@ def get_config_path(base_dir):
         log.warn("%s is deprecated and will not be supported in future. "
                  "Please rename your config file to docker-compose.yml\n" % winner)
 
-    return os.path.join(path, winner)
+    return [os.path.join(path, winner)] + get_default_override_file(path)
+
+
+def get_default_override_file(path):
+    override_filename = os.path.join(path, DEFAULT_OVERRIDE_FILENAME)
+    return [override_filename] if os.path.exists(override_filename) else []
+
+
+def find_candidates_in_parent_dirs(filenames, path):
+    """
+    Given a directory path to start, looks for filenames in the
+    directory, and then each parent directory successively,
+    until found.
+
+    Returns tuple (candidates, path).
+    """
+    candidates = [filename for filename in filenames
+                  if os.path.exists(os.path.join(path, filename))]
+
+    if not candidates:
+        parent_dir = os.path.join(path, '..')
+        if os.path.abspath(parent_dir) != os.path.abspath(path):
+            return find_candidates_in_parent_dirs(filenames, parent_dir)
+
+    return (candidates, path)
 
 
 @validate_top_level_object
@@ -133,29 +178,49 @@ def pre_process_config(config):
     Pre validation checks and processing of the config file to interpolate env
     vars returning a config dict ready to be tested against the schema.
     """
-    config = interpolate_environment_variables(config)
-    return config
+    return interpolate_environment_variables(config)
 
 
 def load(config_details):
-    config, working_dir, filename = config_details
+    """Load the configuration from a working directory and a list of
+    configuration files.  Files are loaded in order, and merged on top
+    of each other to create the final configuration.
 
-    processed_config = pre_process_config(config)
-    validate_against_fields_schema(processed_config)
+    Return a fully interpolated, extended and validated configuration.
+    """
 
-    service_dicts = []
-
-    for service_name, service_dict in list(processed_config.items()):
+    def build_service(filename, service_name, service_dict):
         loader = ServiceLoader(
-            working_dir=working_dir,
-            filename=filename,
-            service_name=service_name,
-            service_dict=service_dict)
+            config_details.working_dir,
+            filename,
+            service_name,
+            service_dict)
         service_dict = loader.make_service_dict()
         validate_paths(service_dict)
-        service_dicts.append(service_dict)
+        return service_dict
 
-    return service_dicts
+    def load_file(filename, config):
+        processed_config = pre_process_config(config)
+        validate_against_fields_schema(processed_config)
+        return [
+            build_service(filename, name, service_config)
+            for name, service_config in processed_config.items()
+        ]
+
+    def merge_services(base, override):
+        all_service_names = set(base) | set(override)
+        return {
+            name: merge_service_dicts(base.get(name, {}), override.get(name, {}))
+            for name in all_service_names
+        }
+
+    config_file = config_details.config_files[0]
+    for next_file in config_details.config_files[1:]:
+        config_file = ConfigFile(
+            config_file.filename,
+            merge_services(config_file.config, next_file.config))
+
+    return load_file(config_file.filename, config_file.config)
 
 
 class ServiceLoader(object):
diff --git a/docs/reference/docker-compose.md b/docs/reference/docker-compose.md
index b43055fb..32fcbe70 100644
--- a/docs/reference/docker-compose.md
+++ b/docs/reference/docker-compose.md
@@ -14,7 +14,7 @@ weight=-2
 
 ```
 Usage:
-  docker-compose [options] [COMMAND] [ARGS...]
+  docker-compose [-f=<arg>...] [options] [COMMAND] [ARGS...]
   docker-compose -h|--help
 
 Options:
@@ -41,20 +41,62 @@ Commands:
   unpause            Unpause services
   up                 Create and start containers
   migrate-to-labels  Recreate containers to add labels
+  version            Show the Docker-Compose version information
 ```
 
-The Docker Compose binary. You use this command to build and manage multiple services in Docker containers.
+The Docker Compose binary. You use this command to build and manage multiple
+services in Docker containers.
 
-Use the `-f` flag to specify the location of a Compose configuration file. This
-flag is optional. If you don't provide this flag. Compose looks for a file named
-`docker-compose.yml` in the  working directory. If the file is not found,
-Compose looks in each parent directory successively, until it finds the file.
+Use the `-f` flag to specify the location of a Compose configuration file. You
+can supply multiple `-f` configuration files. When you supply multiple files,
+Compose combines them into a single configuration. Compose builds the
+configuration in the order you supply the files. Subsequent files override and
+add to their successors.
 
-Use a `-` as the filename to read configuration file from stdin. When stdin is
-used all paths in the configuration are relative to the current working
-directory.
+For example, consider this command line:
+
+```
+$ docker-compose -f docker-compose.yml -f docker-compose.admin.yml run backup_db`
+```
+
+The `docker-compose.yml` file might specify a `webapp` service.
+
+```
+webapp:
+  image: examples/web
+  ports:
+    - "8000:8000"
+  volumes:
+    - "/data"
+```
+
+If the `docker-compose.admin.yml` also specifies this same service, any matching
+fields will override the previous file. New values, add to the `webapp` service
+configuration.
+
+```
+webapp:
+  build: .
+  environment:
+    - DEBUG=1
+```
+
+Use a `-f` with `-` (dash) as the filename to read the configuration from
+stdin. When stdin is used all paths in the configuration are
+relative to the current working directory.
+
+The `-f` flag is optional. If you don't provide this flag on the command line,
+Compose traverses the working directory and its subdirectories looking for a
+`docker-compose.yml` and a `docker-compose.override.yml` file. You must supply
+at least the `docker-compose.yml` file. If both files are present, Compose
+combines the two files into a single configuration. The configuration in the
+`docker-compose.override.yml` file is applied over and in addition to the values
+in the `docker-compose.yml` file.
+
+Each configuration has a project name. If you supply a `-p` flag, you can
+specify a project name. If you don't specify the flag, Compose uses the current
+directory name.
 
-Each configuration can has a project name. If you supply a `-p` flag, you can specify a project name. If you don't specify the flag, Compose uses the current directory name.
 
 ## Where to go next
 
diff --git a/tests/fixtures/override-files/docker-compose.override.yml b/tests/fixtures/override-files/docker-compose.override.yml
new file mode 100644
index 00000000..a03d3d6f
--- /dev/null
+++ b/tests/fixtures/override-files/docker-compose.override.yml
@@ -0,0 +1,6 @@
+
+web:
+    command: "top"
+
+db:
+    command: "top"
diff --git a/tests/fixtures/override-files/docker-compose.yml b/tests/fixtures/override-files/docker-compose.yml
new file mode 100644
index 00000000..8eb43ddb
--- /dev/null
+++ b/tests/fixtures/override-files/docker-compose.yml
@@ -0,0 +1,10 @@
+
+web:
+    image: busybox:latest
+    command: "sleep 200"
+    links:
+        - db
+
+db:
+    image: busybox:latest
+    command: "sleep 200"
diff --git a/tests/fixtures/override-files/extra.yml b/tests/fixtures/override-files/extra.yml
new file mode 100644
index 00000000..7b3ade9c
--- /dev/null
+++ b/tests/fixtures/override-files/extra.yml
@@ -0,0 +1,9 @@
+
+web:
+    links:
+        - db
+        - other
+
+other:
+    image: busybox:latest
+    command: "top"
diff --git a/tests/integration/cli_test.py b/tests/integration/cli_test.py
index 9dadd036..500762e9 100644
--- a/tests/integration/cli_test.py
+++ b/tests/integration/cli_test.py
@@ -9,6 +9,7 @@ from six import StringIO
 
 from .. import mock
 from .testcases import DockerClientTestCase
+from compose.cli.command import get_project
 from compose.cli.errors import UserError
 from compose.cli.main import TopLevelCommand
 from compose.project import NoSuchService
@@ -38,7 +39,7 @@ class CLITestCase(DockerClientTestCase):
         if hasattr(self, '_project'):
             return self._project
 
-        return self.command.get_project()
+        return get_project(self.command.base_dir)
 
     def test_help(self):
         old_base_dir = self.command.base_dir
@@ -72,7 +73,7 @@ class CLITestCase(DockerClientTestCase):
     def test_ps_alternate_composefile(self, mock_stdout):
         config_path = os.path.abspath(
             'tests/fixtures/multiple-composefiles/compose2.yml')
-        self._project = self.command.get_project(config_path)
+        self._project = get_project(self.command.base_dir, [config_path])
 
         self.command.base_dir = 'tests/fixtures/multiple-composefiles'
         self.command.dispatch(['-f', 'compose2.yml', 'up', '-d'], None)
@@ -584,7 +585,6 @@ class CLITestCase(DockerClientTestCase):
         self.assertEqual(get_port(3002), "0.0.0.0:49153")
 
     def test_port_with_scale(self):
-
         self.command.base_dir = 'tests/fixtures/ports-composefile-scale'
         self.command.dispatch(['scale', 'simple=2'], None)
         containers = sorted(
@@ -607,7 +607,7 @@ class CLITestCase(DockerClientTestCase):
     def test_env_file_relative_to_compose_file(self):
         config_path = os.path.abspath('tests/fixtures/env-file/docker-compose.yml')
         self.command.dispatch(['-f', config_path, 'up', '-d'], None)
-        self._project = self.command.get_project(config_path)
+        self._project = get_project(self.command.base_dir, [config_path])
 
         containers = self.project.containers(stopped=True)
         self.assertEqual(len(containers), 1)
@@ -628,6 +628,44 @@ class CLITestCase(DockerClientTestCase):
         self.assertTrue(components[-2:] == ['home-dir', 'my-volume'],
                         msg="Last two components differ: %s, %s" % (actual_host_path, expected_host_path))
 
+    def test_up_with_default_override_file(self):
+        self.command.base_dir = 'tests/fixtures/override-files'
+        self.command.dispatch(['up', '-d'], None)
+
+        containers = self.project.containers()
+        self.assertEqual(len(containers), 2)
+
+        web, db = containers
+        self.assertEqual(web.human_readable_command, 'top')
+        self.assertEqual(db.human_readable_command, 'top')
+
+    def test_up_with_multiple_files(self):
+        self.command.base_dir = 'tests/fixtures/override-files'
+        config_paths = [
+            'docker-compose.yml',
+            'docker-compose.override.yml',
+            'extra.yml',
+
+        ]
+        self._project = get_project(self.command.base_dir, config_paths)
+        self.command.dispatch(
+            [
+                '-f', config_paths[0],
+                '-f', config_paths[1],
+                '-f', config_paths[2],
+                'up', '-d',
+            ],
+            None)
+
+        containers = self.project.containers()
+        self.assertEqual(len(containers), 3)
+
+        web, other, db = containers
+        self.assertEqual(web.human_readable_command, 'top')
+        self.assertTrue({'db', 'other'} <= set(web.links()))
+        self.assertEqual(db.human_readable_command, 'top')
+        self.assertEqual(other.human_readable_command, 'top')
+
     def test_up_with_extends(self):
         self.command.base_dir = 'tests/fixtures/extends'
         self.command.dispatch(['up', '-d'], None)
diff --git a/tests/integration/project_test.py b/tests/integration/project_test.py
index ad49ad10..bd7ecccb 100644
--- a/tests/integration/project_test.py
+++ b/tests/integration/project_test.py
@@ -1,7 +1,7 @@
 from __future__ import unicode_literals
 
 from .testcases import DockerClientTestCase
-from compose import config
+from compose.config import config
 from compose.const import LABEL_PROJECT
 from compose.container import Container
 from compose.project import Project
@@ -9,7 +9,10 @@ from compose.service import ConvergenceStrategy
 
 
 def build_service_dicts(service_config):
-    return config.load(config.ConfigDetails(service_config, 'working_dir', None))
+    return config.load(
+        config.ConfigDetails(
+            'working_dir',
+            [config.ConfigFile(None, service_config)]))
 
 
 class ProjectTest(DockerClientTestCase):
diff --git a/tests/integration/state_test.py b/tests/integration/state_test.py
index 93d0572a..ef7276bd 100644
--- a/tests/integration/state_test.py
+++ b/tests/integration/state_test.py
@@ -9,7 +9,7 @@ import shutil
 import tempfile
 
 from .testcases import DockerClientTestCase
-from compose import config
+from compose.config import config
 from compose.const import LABEL_CONFIG_HASH
 from compose.project import Project
 from compose.service import ConvergenceStrategy
@@ -24,11 +24,13 @@ class ProjectTestCase(DockerClientTestCase):
         return set(project.containers(stopped=True))
 
     def make_project(self, cfg):
+        details = config.ConfigDetails(
+            'working_dir',
+            [config.ConfigFile(None, cfg)])
         return Project.from_dicts(
             name='composetest',
             client=self.client,
-            service_dicts=config.load(config.ConfigDetails(cfg, 'working_dir', None))
-        )
+            service_dicts=config.load(details))
 
 
 class BasicProjectTest(ProjectTestCase):
diff --git a/tests/unit/cli_test.py b/tests/unit/cli_test.py
index d12f4195..321df97a 100644
--- a/tests/unit/cli_test.py
+++ b/tests/unit/cli_test.py
@@ -4,9 +4,12 @@ from __future__ import unicode_literals
 import os
 
 import docker
+import py
 
 from .. import mock
 from .. import unittest
+from compose.cli.command import get_project
+from compose.cli.command import get_project_name
 from compose.cli.docopt_command import NoSuchCommand
 from compose.cli.errors import UserError
 from compose.cli.main import TopLevelCommand
@@ -14,55 +17,45 @@ from compose.service import Service
 
 
 class CLITestCase(unittest.TestCase):
-    def test_default_project_name(self):
-        cwd = os.getcwd()
 
-        try:
-            os.chdir('tests/fixtures/simple-composefile')
-            command = TopLevelCommand()
-            project_name = command.get_project_name('.')
+    def test_default_project_name(self):
+        test_dir = py._path.local.LocalPath('tests/fixtures/simple-composefile')
+        with test_dir.as_cwd():
+            project_name = get_project_name('.')
             self.assertEquals('simplecomposefile', project_name)
-        finally:
-            os.chdir(cwd)
 
     def test_project_name_with_explicit_base_dir(self):
-        command = TopLevelCommand()
-        command.base_dir = 'tests/fixtures/simple-composefile'
-        project_name = command.get_project_name(command.base_dir)
+        base_dir = 'tests/fixtures/simple-composefile'
+        project_name = get_project_name(base_dir)
         self.assertEquals('simplecomposefile', project_name)
 
     def test_project_name_with_explicit_uppercase_base_dir(self):
-        command = TopLevelCommand()
-        command.base_dir = 'tests/fixtures/UpperCaseDir'
-        project_name = command.get_project_name(command.base_dir)
+        base_dir = 'tests/fixtures/UpperCaseDir'
+        project_name = get_project_name(base_dir)
         self.assertEquals('uppercasedir', project_name)
 
     def test_project_name_with_explicit_project_name(self):
-        command = TopLevelCommand()
         name = 'explicit-project-name'
-        project_name = command.get_project_name(None, project_name=name)
+        project_name = get_project_name(None, project_name=name)
         self.assertEquals('explicitprojectname', project_name)
 
     def test_project_name_from_environment_old_var(self):
-        command = TopLevelCommand()
         name = 'namefromenv'
         with mock.patch.dict(os.environ):
             os.environ['FIG_PROJECT_NAME'] = name
-            project_name = command.get_project_name(None)
+            project_name = get_project_name(None)
         self.assertEquals(project_name, name)
 
     def test_project_name_from_environment_new_var(self):
-        command = TopLevelCommand()
         name = 'namefromenv'
         with mock.patch.dict(os.environ):
             os.environ['COMPOSE_PROJECT_NAME'] = name
-            project_name = command.get_project_name(None)
+            project_name = get_project_name(None)
         self.assertEquals(project_name, name)
 
     def test_get_project(self):
-        command = TopLevelCommand()
-        command.base_dir = 'tests/fixtures/longer-filename-composefile'
-        project = command.get_project()
+        base_dir = 'tests/fixtures/longer-filename-composefile'
+        project = get_project(base_dir)
         self.assertEqual(project.name, 'longerfilenamecomposefile')
         self.assertTrue(project.client)
         self.assertTrue(project.services)
diff --git a/tests/unit/config/__init__.py b/tests/unit/config/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/unit/config_test.py b/tests/unit/config/config_test.py
similarity index 91%
rename from tests/unit/config_test.py
rename to tests/unit/config/config_test.py
index ff80270e..79864ec7 100644
--- a/tests/unit/config_test.py
+++ b/tests/unit/config/config_test.py
@@ -5,10 +5,10 @@ import shutil
 import tempfile
 from operator import itemgetter
 
-from .. import mock
-from .. import unittest
 from compose.config import config
 from compose.config.errors import ConfigurationError
+from tests import mock
+from tests import unittest
 
 
 def make_service_dict(name, service_dict, working_dir, filename=None):
@@ -26,10 +26,16 @@ def service_sort(services):
     return sorted(services, key=itemgetter('name'))
 
 
+def build_config_details(contents, working_dir, filename):
+    return config.ConfigDetails(
+        working_dir,
+        [config.ConfigFile(filename, contents)])
+
+
 class ConfigTest(unittest.TestCase):
     def test_load(self):
         service_dicts = config.load(
-            config.ConfigDetails(
+            build_config_details(
                 {
                     'foo': {'image': 'busybox'},
                     'bar': {'image': 'busybox', 'environment': ['FOO=1']},
@@ -57,7 +63,7 @@ class ConfigTest(unittest.TestCase):
     def test_load_throws_error_when_not_dict(self):
         with self.assertRaises(ConfigurationError):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {'web': 'busybox:latest'},
                     'working_dir',
                     'filename.yml'
@@ -68,7 +74,7 @@ class ConfigTest(unittest.TestCase):
         with self.assertRaises(ConfigurationError):
             for invalid_name in ['?not?allowed', ' ', '', '!', '/', '\xe2']:
                 config.load(
-                    config.ConfigDetails(
+                    build_config_details(
                         {invalid_name: {'image': 'busybox'}},
                         'working_dir',
                         'filename.yml'
@@ -79,17 +85,54 @@ class ConfigTest(unittest.TestCase):
         expected_error_msg = "Service name: 1 needs to be a string, eg '1'"
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {1: {'image': 'busybox'}},
                     'working_dir',
                     'filename.yml'
                 )
             )
 
+    def test_load_with_multiple_files(self):
+        base_file = config.ConfigFile(
+            'base.yaml',
+            {
+                'web': {
+                    'image': 'example/web',
+                    'links': ['db'],
+                },
+                'db': {
+                    'image': 'example/db',
+                },
+            })
+        override_file = config.ConfigFile(
+            'override.yaml',
+            {
+                'web': {
+                    'build': '/',
+                    'volumes': ['/home/user/project:/code'],
+                },
+            })
+        details = config.ConfigDetails('.', [base_file, override_file])
+
+        service_dicts = config.load(details)
+        expected = [
+            {
+                'name': 'web',
+                'build': '/',
+                'links': ['db'],
+                'volumes': ['/home/user/project:/code'],
+            },
+            {
+                'name': 'db',
+                'image': 'example/db',
+            },
+        ]
+        self.assertEqual(service_sort(service_dicts), service_sort(expected))
+
     def test_config_valid_service_names(self):
         for valid_name in ['_', '-', '.__.', '_what-up.', 'what_.up----', 'whatup']:
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {valid_name: {'image': 'busybox'}},
                     'tests/fixtures/extends',
                     'common.yml'
@@ -101,7 +144,7 @@ class ConfigTest(unittest.TestCase):
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             for invalid_ports in [{"1": "8000"}, False, 0, "8000", 8000, ["8000", "8000"]]:
                 config.load(
-                    config.ConfigDetails(
+                    build_config_details(
                         {'web': {'image': 'busybox', 'ports': invalid_ports}},
                         'working_dir',
                         'filename.yml'
@@ -112,7 +155,7 @@ class ConfigTest(unittest.TestCase):
         valid_ports = [["8000", "9000"], ["8000/8050"], ["8000"], [8000], ["49153-49154:3002-3003"]]
         for ports in valid_ports:
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {'web': {'image': 'busybox', 'ports': ports}},
                     'working_dir',
                     'filename.yml'
@@ -123,7 +166,7 @@ class ConfigTest(unittest.TestCase):
         expected_error_msg = "(did you mean 'privileged'?)"
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {
                         'foo': {'image': 'busybox', 'privilige': 'something'},
                     },
@@ -136,7 +179,7 @@ class ConfigTest(unittest.TestCase):
         expected_error_msg = "Service 'foo' has both an image and build path specified."
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {
                         'foo': {'image': 'busybox', 'build': '.'},
                     },
@@ -149,7 +192,7 @@ class ConfigTest(unittest.TestCase):
         expected_error_msg = "Service 'foo' configuration key 'links' contains an invalid type, it should be an array"
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {
                         'foo': {'image': 'busybox', 'links': 'an_link'},
                     },
@@ -162,7 +205,7 @@ class ConfigTest(unittest.TestCase):
         expected_error_msg = "Top level object needs to be a dictionary."
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     ['foo', 'lol'],
                     'tests/fixtures/extends',
                     'filename.yml'
@@ -173,7 +216,7 @@ class ConfigTest(unittest.TestCase):
         expected_error_msg = "has non-unique elements"
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {
                         'web': {'build': '.', 'devices': ['/dev/foo:/dev/foo', '/dev/foo:/dev/foo']}
                     },
@@ -187,7 +230,7 @@ class ConfigTest(unittest.TestCase):
         expected_error_msg += ", which is an invalid type, it should be a string"
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {
                         'web': {'build': '.', 'command': [1]}
                     },
@@ -200,7 +243,7 @@ class ConfigTest(unittest.TestCase):
         expected_error_msg = "Service 'web' has both an image and alternate Dockerfile."
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {'web': {'image': 'busybox', 'dockerfile': 'Dockerfile.alt'}},
                     'working_dir',
                     'filename.yml'
@@ -212,7 +255,7 @@ class ConfigTest(unittest.TestCase):
 
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {'web': {
                         'image': 'busybox',
                         'extra_hosts': 'somehost:162.242.195.82'
@@ -227,7 +270,7 @@ class ConfigTest(unittest.TestCase):
 
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {'web': {
                         'image': 'busybox',
                         'extra_hosts': [
@@ -244,7 +287,7 @@ class ConfigTest(unittest.TestCase):
         expose_values = [["8000"], [8000]]
         for expose in expose_values:
             service = config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {'web': {
                         'image': 'busybox',
                         'expose': expose
@@ -259,7 +302,7 @@ class ConfigTest(unittest.TestCase):
         entrypoint_values = [["sh"], "sh"]
         for entrypoint in entrypoint_values:
             service = config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {'web': {
                         'image': 'busybox',
                         'entrypoint': entrypoint
@@ -274,7 +317,7 @@ class ConfigTest(unittest.TestCase):
     def test_logs_warning_for_boolean_in_environment(self, mock_logging):
         expected_warning_msg = "Warning: There is a boolean value, True in the 'environment' key."
         config.load(
-            config.ConfigDetails(
+            build_config_details(
                 {'web': {
                     'image': 'busybox',
                     'environment': {'SHOW_STUFF': True}
@@ -292,7 +335,7 @@ class ConfigTest(unittest.TestCase):
 
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {'web': {
                         'image': 'busybox',
                         'environment': {'---': 'nope'}
@@ -331,16 +374,16 @@ class InterpolationTest(unittest.TestCase):
     def test_unset_variable_produces_warning(self):
         os.environ.pop('FOO', None)
         os.environ.pop('BAR', None)
-        config_details = config.ConfigDetails(
-            config={
+        config_details = build_config_details(
+            {
                 'web': {
                     'image': '${FOO}',
                     'command': '${BAR}',
                     'container_name': '${BAR}',
                 },
             },
-            working_dir='.',
-            filename=None,
+            '.',
+            None,
         )
 
         with mock.patch('compose.config.interpolation.log') as log:
@@ -355,7 +398,7 @@ class InterpolationTest(unittest.TestCase):
     def test_invalid_interpolation(self):
         with self.assertRaises(config.ConfigurationError) as cm:
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {'web': {'image': '${'}},
                     'working_dir',
                     'filename.yml'
@@ -371,10 +414,10 @@ class InterpolationTest(unittest.TestCase):
     def test_volume_binding_with_environment_variable(self):
         os.environ['VOLUME_PATH'] = '/host/path'
         d = config.load(
-            config.ConfigDetails(
-                config={'foo': {'build': '.', 'volumes': ['${VOLUME_PATH}:/container/path']}},
-                working_dir='.',
-                filename=None,
+            build_config_details(
+                {'foo': {'build': '.', 'volumes': ['${VOLUME_PATH}:/container/path']}},
+                '.',
+                None,
             )
         )[0]
         self.assertEqual(d['volumes'], ['/host/path:/container/path'])
@@ -649,7 +692,7 @@ class MemoryOptionsTest(unittest.TestCase):
         )
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {
                         'foo': {'image': 'busybox', 'memswap_limit': 2000000},
                     },
@@ -660,7 +703,7 @@ class MemoryOptionsTest(unittest.TestCase):
 
     def test_validation_with_correct_memswap_values(self):
         service_dict = config.load(
-            config.ConfigDetails(
+            build_config_details(
                 {'foo': {'image': 'busybox', 'mem_limit': 1000000, 'memswap_limit': 2000000}},
                 'tests/fixtures/extends',
                 'common.yml'
@@ -670,7 +713,7 @@ class MemoryOptionsTest(unittest.TestCase):
 
     def test_memswap_can_be_a_string(self):
         service_dict = config.load(
-            config.ConfigDetails(
+            build_config_details(
                 {'foo': {'image': 'busybox', 'mem_limit': "1G", 'memswap_limit': "512M"}},
                 'tests/fixtures/extends',
                 'common.yml'
@@ -780,26 +823,26 @@ class EnvTest(unittest.TestCase):
         os.environ['CONTAINERENV'] = '/host/tmp'
 
         service_dict = config.load(
-            config.ConfigDetails(
-                config={'foo': {'build': '.', 'volumes': ['$HOSTENV:$CONTAINERENV']}},
-                working_dir="tests/fixtures/env",
-                filename=None,
+            build_config_details(
+                {'foo': {'build': '.', 'volumes': ['$HOSTENV:$CONTAINERENV']}},
+                "tests/fixtures/env",
+                None,
             )
         )[0]
         self.assertEqual(set(service_dict['volumes']), set(['/tmp:/host/tmp']))
 
         service_dict = config.load(
-            config.ConfigDetails(
-                config={'foo': {'build': '.', 'volumes': ['/opt${HOSTENV}:/opt${CONTAINERENV}']}},
-                working_dir="tests/fixtures/env",
-                filename=None,
+            build_config_details(
+                {'foo': {'build': '.', 'volumes': ['/opt${HOSTENV}:/opt${CONTAINERENV}']}},
+                "tests/fixtures/env",
+                None,
             )
         )[0]
         self.assertEqual(set(service_dict['volumes']), set(['/opt/tmp:/opt/host/tmp']))
 
 
 def load_from_filename(filename):
-    return config.load(config.find('.', filename))
+    return config.load(config.find('.', [filename]))
 
 
 class ExtendsTest(unittest.TestCase):
@@ -885,7 +928,7 @@ class ExtendsTest(unittest.TestCase):
     def test_extends_validation_empty_dictionary(self):
         with self.assertRaisesRegexp(ConfigurationError, 'service'):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {
                         'web': {'image': 'busybox', 'extends': {}},
                     },
@@ -897,7 +940,7 @@ class ExtendsTest(unittest.TestCase):
     def test_extends_validation_missing_service_key(self):
         with self.assertRaisesRegexp(ConfigurationError, "'service' is a required property"):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {
                         'web': {'image': 'busybox', 'extends': {'file': 'common.yml'}},
                     },
@@ -910,7 +953,7 @@ class ExtendsTest(unittest.TestCase):
         expected_error_msg = "Unsupported config option for 'web' service: 'rogue_key'"
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {
                         'web': {
                             'image': 'busybox',
@@ -930,7 +973,7 @@ class ExtendsTest(unittest.TestCase):
         expected_error_msg = "Service 'web' configuration key 'extends' 'file' contains an invalid type"
         with self.assertRaisesRegexp(ConfigurationError, expected_error_msg):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {
                         'web': {
                             'image': 'busybox',
@@ -955,7 +998,7 @@ class ExtendsTest(unittest.TestCase):
 
     def test_extends_validation_valid_config(self):
         service = config.load(
-            config.ConfigDetails(
+            build_config_details(
                 {
                     'web': {'image': 'busybox', 'extends': {'service': 'web', 'file': 'common.yml'}},
                 },
@@ -1093,7 +1136,7 @@ class BuildPathTest(unittest.TestCase):
     def test_nonexistent_path(self):
         with self.assertRaises(ConfigurationError):
             config.load(
-                config.ConfigDetails(
+                build_config_details(
                     {
                         'foo': {'build': 'nonexistent.path'},
                     },
@@ -1124,7 +1167,7 @@ class BuildPathTest(unittest.TestCase):
         self.assertEquals(service_dict, [{'name': 'foo', 'build': self.abs_context_path}])
 
 
-class GetConfigPathTestCase(unittest.TestCase):
+class GetDefaultConfigFilesTestCase(unittest.TestCase):
 
     files = [
         'docker-compose.yml',
@@ -1134,25 +1177,21 @@ class GetConfigPathTestCase(unittest.TestCase):
     ]
 
     def test_get_config_path_default_file_in_basedir(self):
-        files = self.files
-        self.assertEqual('docker-compose.yml', get_config_filename_for_files(files[0:]))
-        self.assertEqual('docker-compose.yaml', get_config_filename_for_files(files[1:]))
-        self.assertEqual('fig.yml', get_config_filename_for_files(files[2:]))
-        self.assertEqual('fig.yaml', get_config_filename_for_files(files[3:]))
+        for index, filename in enumerate(self.files):
+            self.assertEqual(
+                filename,
+                get_config_filename_for_files(self.files[index:]))
         with self.assertRaises(config.ComposeFileNotFound):
             get_config_filename_for_files([])
 
     def test_get_config_path_default_file_in_parent_dir(self):
         """Test with files placed in the subdir"""
-        files = self.files
 
         def get_config_in_subdir(files):
             return get_config_filename_for_files(files, subdir=True)
 
-        self.assertEqual('docker-compose.yml', get_config_in_subdir(files[0:]))
-        self.assertEqual('docker-compose.yaml', get_config_in_subdir(files[1:]))
-        self.assertEqual('fig.yml', get_config_in_subdir(files[2:]))
-        self.assertEqual('fig.yaml', get_config_in_subdir(files[3:]))
+        for index, filename in enumerate(self.files):
+            self.assertEqual(filename, get_config_in_subdir(self.files[index:]))
         with self.assertRaises(config.ComposeFileNotFound):
             get_config_in_subdir([])
 
@@ -1170,6 +1209,7 @@ def get_config_filename_for_files(filenames, subdir=None):
             base_dir = tempfile.mkdtemp(dir=project_dir)
         else:
             base_dir = project_dir
-        return os.path.basename(config.get_config_path(base_dir))
+        filename, = config.get_default_config_files(base_dir)
+        return os.path.basename(filename)
     finally:
         shutil.rmtree(project_dir)