diff --git a/docs/config.md b/docs/config.md
new file mode 100644
index 00000000..363fed7c
--- /dev/null
+++ b/docs/config.md
@@ -0,0 +1,211 @@
+Starlette encourages a strict separation of configuration from code,
+following [the twelve-factor pattern][twelve-factor].
+
+Configuration should be stored in environment variables, or in a ".env" file
+that is not committed to source control.
+
+**app.py**:
+
+```python
+from starlette.applications import Starlette
+from starlette.config import Config
+from starlette.datastructures import DatabaseURL, Secret
+
+config = Config(".env")
+
+DEBUG = config('DEBUG', cast=bool, default=False)
+DATABASE_URL = config('DATABASE_URL', cast=DatabaseURL)
+SECRET_KEY = config('SECRET_KEY', cast=Secret)
+
+app = Starlette()
+app.debug = DEBUG
+...
+```
+
+**.env**:
+
+```shell
+# Don't commit this to source control.
+# Eg. Include ".env" in your `.gitignore` file.
+DEBUG=True
+DATABASE_URL=postgresql://localhost/myproject
+SECRET_KEY=43n080musdfjt54t-09sdgr
+```
+
+## Configuration precedence
+
+The order in which configuration values are read is:
+
+* From an environment variable.
+* From the ".env" file.
+* The default value given in `config`.
+
+If none of those match, then `config(...)` will raise an error.
+
+## Secrets
+
+For sensitive keys, the `Secret` class is useful, since it prevents the value from
+leaking out into tracebacks or logging.
+
+To get the value of a `Secret` instance, you must explicitly cast it to a string.
+You should only do this at the point at which the value is used.
+
+```python
+>>> from myproject import settings
+>>> print(settings.SECRET_KEY)
+Secret('**********')
+>>> str(settings.SECRET_KEY)
+'98n349$%8b8-7yjn0n8y93T$23r'
+```
+
+Similarly, the `URL` and `DatabaseURL` class will hide any password component
+in their representations.
+
+```python
+>>> from myproject import settings
+>>> print(settings.DATABASE_URL)
+DatabaseURL('postgresql://admin:**********@192.168.0.8/my-application')
+>>> str(settings.SECRET_KEY)
+'98n349$%8b8-7yjn0n8y93T$23r'
+```
+
+## Reading or modifying the environment
+
+In some cases you might want to read or modify the environment variables programmatically.
+This is particularly useful in testing, where you may want to override particular
+keys in the environment.
+
+Rather than reading or writing from `os.environ`, you should use Starlette's
+`environ` instance. This instance is a mapping onto the standard `os.environ`
+that additionally protects you by raising an error if any environment variable
+is set *after* the point that it has already been read by the configuration.
+
+If you're using `pytest`, then you can setup any initial environment in
+`tests/conftest.py`.
+
+**tests/conftest.py**:
+
+```python
+from starlette.config import environ
+
+environ['TESTING'] = 'TRUE'
+```
+
+## A full example
+
+Structuring large applications can be complex. You need proper separation of
+configuration and code, database isolation during tests, separate test and
+production databases, etc...
+
+Here we'll take a look at a complete example, that demonstrates how
+we can start to structure an application.
+
+First, let's keep our settings, our database table definitions, and our
+application logic separated:
+
+**myproject/settings.py**:
+
+```python
+from starlette.config import Config
+from starlette.datastructures import DatabaseURL, Secret
+
+config = Config(".env")
+
+DEBUG = config('DEBUG', cast=bool, default=False)
+TESTING = config('TESTING', cast=bool, default=False)
+SECRET_KEY = config('SECRET_KEY', cast=Secret)
+
+DATABASE_URL = config('DATABASE_URL', cast=DatabaseURL)
+if TESTING:
+    DATABASE_URL = DATABASE_URL.replace(database='test_' + DATABASE_URL.database)
+```
+
+**myproject/tables.py**:
+
+```python
+import sqlalchemy
+
+# Database table definitions.
+metadata = sqlalchemy.MetaData()
+
+organisations = sqlalchemy.Table(
+    ...
+)
+```
+
+**myproject/app.py**
+
+```python
+from starlette.applications import Starlette
+from starlette.middleware.database import DatabaseMiddleware
+from starlette.middleware.session import SessionMiddleware
+from myproject import settings
+
+
+app = Starlette()
+
+app.debug = settings.DEBUG
+
+app.add_middleware(
+    SessionMiddleware,
+    secret_key=settings.SECRET_KEY,
+)
+app.add_middleware(
+    DatabaseMiddleware,
+    database_url=settings.DATABASE_URL,
+    rollback_on_shutdown=settings.TESTING
+)
+
+@app.route('/', methods=['GET'])
+async def homepage(request):
+    ...
+```
+
+Now let's deal with our test configuration.
+We'd like to create a new test database every time the test suite runs,
+and drop it once the tests complete. We'd also like to ensure
+
+**tests/conftest.py**:
+
+```python
+from starlette.config import environ
+from starlette.testclient import TestClient
+from sqlalchemy import create_engine
+from sqlalchemy_utils import database_exists, create_database
+
+# This line would raise an error if we use it after 'settings' has been imported.
+environ['TESTING'] = 'TRUE'
+
+from myproject import settings
+from myproject.app import app
+from myproject.tables import metadata
+
+
+@pytest.fixture(autouse=True, scope="session")
+def setup_test_database():
+    """
+    Create a clean test database every time the tests are run.
+    """
+    engine = create_engine(settings.DATABASE_URL)
+    assert not database_exists(engine.url), 'Test database already exists. Aborting tests.'
+    create_database(settings.DATABASE_URL)  # Create the test database.
+    metadata.create_all(engine)             # Create the tables.
+    yield                                   # Run the tests.
+    drop_database(settings.DATABASE_URL)    # Drop the test database.
+
+
+@pytest.fixture()
+def client():
+    """
+    Make a 'client' fixture available to test cases.
+    """
+    # Our fixture is created within a context manager. This ensures that
+    # application startup and shutdown run for every test case.
+    #
+    # Because we've configured the DatabaseMiddleware with `rollback_on_shutdown`
+    # we'll get a complete rollback to the initial state after each test case runs.
+    async with TestClient(app) as test_client:
+        yield test_client
+```
+
+[twelve-factor]: https://12factor.net/config
diff --git a/docs/database.md b/docs/database.md
index c6a54c99..70ebab67 100644
--- a/docs/database.md
+++ b/docs/database.md
@@ -14,10 +14,17 @@ Here's a complete example, that includes table definitions, installing the
 import os
 import sqlalchemy
 from starlette.applications import Starlette
+from starlette.config import Config
 from starlette.middleware.database import DatabaseMiddleware
 from starlette.responses import JSONResponse
 
 
+# Configuration from environment variables or '.env' file.
+config = Config('.env')
+DATABASE_URL = config('DATABASE_URL')
+
+
+# Database table definitions.
 metadata = sqlalchemy.MetaData()
 
 notes = sqlalchemy.Table(
@@ -28,10 +35,13 @@ notes = sqlalchemy.Table(
     sqlalchemy.Column("completed", sqlalchemy.Boolean),
 )
 
+
+# Application setup.
 app = Starlette()
-app.add_middleware(DatabaseMiddleware, database_url=os.environ['DATABASE_URL'])
+app.add_middleware(DatabaseMiddleware, database_url=DATABASE_URL)
 
 
+# Endpoints.
 @app.route("/notes", methods=["GET"])
 async def list_notes(request):
     query = notes.select()
diff --git a/docs/release-notes.md b/docs/release-notes.md
index 6ddc34cc..9b8840cc 100644
--- a/docs/release-notes.md
+++ b/docs/release-notes.md
@@ -1,3 +1,13 @@
+## 0.9.4
+
+* Add `config.environ`.
+* Add `datastructures.Secret`.
+* Add `datastructures.DatabaseURL`.
+
+## 0.9.3
+
+* Add `config.Config(".env")`
+
 ## 0.9.2
 
 * Add optional database support.
diff --git a/mkdocs.yml b/mkdocs.yml
index 16dac44d..7bbb0fde 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -25,6 +25,7 @@ nav:
     - Events: 'events.md'
     - Background Tasks: 'background.md'
     - Exceptions: 'exceptions.md'
+    - Configuration: 'config.md'
     - Test Client: 'testclient.md'
     - Release Notes: 'release-notes.md'
 
diff --git a/starlette/__init__.py b/starlette/__init__.py
index c5981731..e94731c0 100644
--- a/starlette/__init__.py
+++ b/starlette/__init__.py
@@ -1 +1 @@
-__version__ = "0.9.3"
+__version__ = "0.9.4"
diff --git a/starlette/config.py b/starlette/config.py
index 8adcc684..03571bdf 100644
--- a/starlette/config.py
+++ b/starlette/config.py
@@ -55,6 +55,11 @@ class Config:
         if env_file is not None and os.path.isfile(env_file):
             self.file_values = self._read_file(env_file)
 
+    def __call__(
+        self, key: str, cast: type = None, default: typing.Any = undefined
+    ) -> typing.Any:
+        return self.get(key, cast, default)
+
     def get(
         self, key: str, cast: type = None, default: typing.Any = undefined
     ) -> typing.Any:
@@ -65,7 +70,7 @@ class Config:
             value = self.file_values[key]
             return self._perform_cast(key, value, cast)
         if default is not undefined:
-            return default
+            return self._perform_cast(key, default, cast)
         raise KeyError("Config '%s' is missing, and has no default." % key)
 
     def _read_file(self, file_name: str) -> typing.Dict[str, str]:
@@ -80,7 +85,9 @@ class Config:
                     file_values[key] = value
         return file_values
 
-    def _perform_cast(self, key: str, value: str, cast: type = None) -> typing.Any:
+    def _perform_cast(
+        self, key: str, value: typing.Any, cast: type = None
+    ) -> typing.Any:
         if cast is None or value is None:
             return value
         elif cast is bool and isinstance(value, str):
diff --git a/starlette/datastructures.py b/starlette/datastructures.py
index 62c37ae9..50f0d5bc 100644
--- a/starlette/datastructures.py
+++ b/starlette/datastructures.py
@@ -133,12 +133,22 @@ class URL:
 
 class DatabaseURL(URL):
     @property
-    def name(self) -> str:
+    def database(self) -> str:
         return self.path.lstrip("/")
 
+    @property
+    def dialect(self) -> str:
+        return self.scheme.split("+")[0]
+
+    @property
+    def driver(self) -> str:
+        if "+" not in self.scheme:
+            return ""
+        return self.scheme.split("+", 1)[1]
+
     def replace(self, **kwargs: typing.Any) -> "URL":
-        if "name" in kwargs:
-            kwargs["path"] = "/" + kwargs.pop("name")
+        if "database" in kwargs:
+            kwargs["path"] = "/" + kwargs.pop("database")
         return super().replace(**kwargs)
 
 
diff --git a/starlette/middleware/database.py b/starlette/middleware/database.py
index fc15f2df..3c64b42f 100644
--- a/starlette/middleware/database.py
+++ b/starlette/middleware/database.py
@@ -29,7 +29,9 @@ class DatabaseMiddleware:
     ) -> DatabaseBackend:
         if isinstance(database_url, str):
             database_url = DatabaseURL(database_url)
-        assert database_url.scheme == "postgresql"
+        assert (
+            database_url.dialect == "postgresql"
+        ), "Currently only postgresql is supported."
         from starlette.database.postgres import PostgresBackend
 
         return PostgresBackend(database_url)
diff --git a/tests/test_config.py b/tests/test_config.py
index 4fb2027d..1381772c 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -20,14 +20,14 @@ def test_config(tmpdir):
 
     config = Config(path, environ={"DEBUG": "true"})
 
-    DEBUG = config.get("DEBUG", cast=bool)
-    DATABASE_URL = config.get("DATABASE_URL", cast=DatabaseURL)
-    REQUEST_TIMEOUT = config.get("REQUEST_TIMEOUT", cast=int, default=10)
-    REQUEST_HOSTNAME = config.get("REQUEST_HOSTNAME")
-    SECRET_KEY = config.get("SECRET_KEY", cast=Secret)
+    DEBUG = config("DEBUG", cast=bool)
+    DATABASE_URL = config("DATABASE_URL", cast=DatabaseURL)
+    REQUEST_TIMEOUT = config("REQUEST_TIMEOUT", cast=int, default=10)
+    REQUEST_HOSTNAME = config("REQUEST_HOSTNAME")
+    SECRET_KEY = config("SECRET_KEY", cast=Secret)
 
     assert DEBUG is True
-    assert DATABASE_URL.name == "database_name"
+    assert DATABASE_URL.database == "database_name"
     assert REQUEST_TIMEOUT == 10
     assert REQUEST_HOSTNAME == "example.com"
     assert repr(SECRET_KEY) == "Secret('**********')"
diff --git a/tests/test_datastructures.py b/tests/test_datastructures.py
index 9560630e..666aabd0 100644
--- a/tests/test_datastructures.py
+++ b/tests/test_datastructures.py
@@ -46,10 +46,18 @@ def test_hidden_password():
 
 def test_database_url():
     u = DatabaseURL("postgresql://username:password@localhost/mydatabase")
-    u = u.replace(name="test_" + u.name)
-    assert u.name == "test_mydatabase"
+    u = u.replace(database="test_" + u.database)
+    assert u.database == "test_mydatabase"
     assert str(u) == "postgresql://username:password@localhost/test_mydatabase"
 
+    u = DatabaseURL("postgresql://localhost/mydatabase")
+    assert u.dialect == "postgresql"
+    assert u.driver == ""
+
+    u = DatabaseURL("postgresql+asyncpg://localhost/mydatabase")
+    assert u.dialect == "postgresql"
+    assert u.driver == "asyncpg"
+
 
 def test_url_from_scope():
     u = URL(