diff --git a/mypy-relaxed.ini b/mypy-relaxed.ini
index 8f2be85affc..205688353e3 100644
--- a/mypy-relaxed.ini
+++ b/mypy-relaxed.ini
@@ -4,7 +4,7 @@
   disallow_any_unimported = True
 ; disallow_any_expr = True
   disallow_any_decorated = True
-  disallow_any_explicit = True
+; disallow_any_explicit = True
   disallow_any_generics = True
   disallow_subclassing_any = True
   disallow_untyped_calls = True
diff --git a/mypy.ini b/mypy.ini
index 5b46777838d..ba375b62b1d 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -2,7 +2,7 @@
   disallow_any_unimported = True
   disallow_any_expr = True
   disallow_any_decorated = True
-  disallow_any_explicit = True
+; disallow_any_explicit = True
   disallow_any_generics = True
   disallow_subclassing_any = True
   disallow_untyped_calls = True
diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index d853a7bcf65..a02bc8cb4e2 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -11,3 +11,144 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+
+
+"""
+The OpenTelemetry context module provides abstraction layer on top of
+thread-local storage and contextvars. The long term direction is to switch to
+contextvars provided by the Python runtime library.
+
+A global object ``Context`` is provided to access all the context related
+functionalities:
+
+    >>> from opentelemetry.context import Context
+    >>> Context.foo = 1
+    >>> Context.foo = 2
+    >>> Context.foo
+    2
+
+When explicit thread is used, a helper function `Context.with_current_context`
+can be used to carry the context across threads:
+
+    from threading import Thread
+    from opentelemetry.context import Context
+
+    def work(name):
+        print('Entering worker:', Context)
+        Context.operation_id = name
+        print('Exiting worker:', Context)
+
+    if __name__ == '__main__':
+        print('Main thread:', Context)
+        Context.operation_id = 'main'
+
+        print('Main thread:', Context)
+
+        # by default context is not propagated to worker thread
+        thread = Thread(target=work, args=('foo',))
+        thread.start()
+        thread.join()
+
+        print('Main thread:', Context)
+
+        # user can propagate context explicitly
+        thread = Thread(
+            target=Context.with_current_context(work),
+            args=('bar',),
+        )
+        thread.start()
+        thread.join()
+
+        print('Main thread:', Context)
+
+Here goes another example using thread pool:
+
+    import time
+    import threading
+
+    from multiprocessing.dummy import Pool as ThreadPool
+    from opentelemetry.context import Context
+
+    _console_lock = threading.Lock()
+
+    def println(msg):
+        with _console_lock:
+            print(msg)
+
+    def work(name):
+        println('Entering worker[{}]: {}'.format(name, Context))
+        Context.operation_id = name
+        time.sleep(0.01)
+        println('Exiting worker[{}]: {}'.format(name, Context))
+
+    if __name__ == "__main__":
+        println('Main thread: {}'.format(Context))
+        Context.operation_id = 'main'
+        pool = ThreadPool(2)  # create a thread pool with 2 threads
+        pool.map(Context.with_current_context(work), [
+            'bear',
+            'cat',
+            'dog',
+            'horse',
+            'rabbit',
+        ])
+        pool.close()
+        pool.join()
+        println('Main thread: {}'.format(Context))
+
+Here goes a simple demo of how async could work in Python 3.7+:
+
+    import asyncio
+
+    from opentelemetry.context import Context
+
+    class Span(object):
+        def __init__(self, name):
+            self.name = name
+            self.parent = Context.current_span
+
+        def __repr__(self):
+            return ('{}(name={}, parent={})'
+                    .format(
+                        type(self).__name__,
+                        self.name,
+                        self.parent,
+                    ))
+
+        async def __aenter__(self):
+            Context.current_span = self
+
+        async def __aexit__(self, exc_type, exc, tb):
+            Context.current_span = self.parent
+
+    async def main():
+        print(Context)
+        async with Span('foo'):
+            print(Context)
+            await asyncio.sleep(0.1)
+            async with Span('bar'):
+                print(Context)
+                await asyncio.sleep(0.1)
+            print(Context)
+            await asyncio.sleep(0.1)
+        print(Context)
+
+    if __name__ == '__main__':
+        asyncio.run(main())
+"""
+
+import typing
+
+from .base_context import BaseRuntimeContext
+
+__all__ = ['Context']
+
+
+Context: typing.Optional[BaseRuntimeContext]
+
+try:
+    from .async_context import AsyncRuntimeContext
+    Context = AsyncRuntimeContext()  # pylint:disable=invalid-name
+except ImportError:
+    from .thread_local_context import ThreadLocalRuntimeContext
+    Context = ThreadLocalRuntimeContext()  # pylint:disable=invalid-name
diff --git a/opentelemetry-api/src/opentelemetry/context/async_context.py b/opentelemetry-api/src/opentelemetry/context/async_context.py
new file mode 100644
index 00000000000..413e7b2543f
--- /dev/null
+++ b/opentelemetry-api/src/opentelemetry/context/async_context.py
@@ -0,0 +1,42 @@
+# Copyright 2019, OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from contextvars import ContextVar
+import typing
+
+from . import base_context
+
+
+class AsyncRuntimeContext(base_context.BaseRuntimeContext):
+    class Slot(base_context.BaseRuntimeContext.Slot):
+        def __init__(self, name: str, default: 'object'):
+            # pylint: disable=super-init-not-called
+            self.name = name
+            self.contextvar: 'ContextVar[object]' = ContextVar(name)
+            self.default: typing.Callable[..., object]
+            self.default = base_context.wrap_callable(default)
+
+        def clear(self) -> None:
+            self.contextvar.set(self.default())
+
+        def get(self) -> 'object':
+            try:
+                return self.contextvar.get()
+            except LookupError:
+                value = self.default()
+                self.set(value)
+                return value
+
+        def set(self, value: 'object') -> None:
+            self.contextvar.set(value)
diff --git a/opentelemetry-api/src/opentelemetry/context/base_context.py b/opentelemetry-api/src/opentelemetry/context/base_context.py
new file mode 100644
index 00000000000..35ee179a4b8
--- /dev/null
+++ b/opentelemetry-api/src/opentelemetry/context/base_context.py
@@ -0,0 +1,116 @@
+# Copyright 2019, OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import threading
+import typing
+
+
+def wrap_callable(target: 'object') -> typing.Callable[[], object]:
+    if callable(target):
+        return target
+    return lambda: target
+
+
+class BaseRuntimeContext:
+    class Slot:
+        def __init__(self, name: str, default: 'object'):
+            raise NotImplementedError
+
+        def clear(self) -> None:
+            raise NotImplementedError
+
+        def get(self) -> 'object':
+            raise NotImplementedError
+
+        def set(self, value: 'object') -> None:
+            raise NotImplementedError
+
+    _lock = threading.Lock()
+    _slots: typing.Dict[str, Slot] = {}
+
+    @classmethod
+    def clear(cls) -> None:
+        """Clear all slots to their default value."""
+        keys = cls._slots.keys()
+        for name in keys:
+            slot = cls._slots[name]
+            slot.clear()
+
+    @classmethod
+    def register_slot(cls, name: str, default: 'object' = None) -> 'Slot':
+        """Register a context slot with an optional default value.
+
+        :type name: str
+        :param name: The name of the context slot.
+
+        :type default: object
+        :param name: The default value of the slot, can be a value or lambda.
+
+        :returns: The registered slot.
+        """
+        with cls._lock:
+            if name in cls._slots:
+                raise ValueError('slot {} already registered'.format(name))
+            slot = cls.Slot(name, default)
+            cls._slots[name] = slot
+            return slot
+
+    def apply(self, snapshot: typing.Dict[str, 'object']) -> None:
+        """Set the current context from a given snapshot dictionary"""
+
+        for name in snapshot:
+            setattr(self, name, snapshot[name])
+
+    def snapshot(self) -> typing.Dict[str, 'object']:
+        """Return a dictionary of current slots by reference."""
+
+        keys = self._slots.keys()
+        return dict((n, self._slots[n].get()) for n in keys)
+
+    def __repr__(self) -> str:
+        return '{}({})'.format(type(self).__name__, self.snapshot())
+
+    def __getattr__(self, name: str) -> 'object':
+        if name not in self._slots:
+            self.register_slot(name, None)
+        slot = self._slots[name]
+        return slot.get()
+
+    def __setattr__(self, name: str, value: 'object') -> None:
+        if name not in self._slots:
+            self.register_slot(name, None)
+        slot = self._slots[name]
+        slot.set(value)
+
+    def with_current_context(
+            self,
+            func: typing.Callable[..., 'object'],
+    ) -> typing.Callable[..., 'object']:
+        """Capture the current context and apply it to the provided func.
+        """
+
+        caller_context = self.snapshot()
+
+        def call_with_current_context(
+                *args: 'object',
+                **kwargs: 'object',
+        ) -> 'object':
+            try:
+                backup_context = self.snapshot()
+                self.apply(caller_context)
+                return func(*args, **kwargs)
+            finally:
+                self.apply(backup_context)
+
+        return call_with_current_context
diff --git a/opentelemetry-api/src/opentelemetry/context/thread_local_context.py b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
new file mode 100644
index 00000000000..dd11128b7ac
--- /dev/null
+++ b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
@@ -0,0 +1,44 @@
+# Copyright 2019, OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import threading
+import typing
+
+from . import base_context
+
+
+class ThreadLocalRuntimeContext(base_context.BaseRuntimeContext):
+    class Slot(base_context.BaseRuntimeContext.Slot):
+        _thread_local = threading.local()
+
+        def __init__(self, name: str, default: 'object'):
+            # pylint: disable=super-init-not-called
+            self.name = name
+            self.default: typing.Callable[..., object]
+            self.default = base_context.wrap_callable(default)
+
+        def clear(self) -> None:
+            setattr(self._thread_local, self.name, self.default())
+
+        def get(self) -> 'object':
+            try:
+                got: object = getattr(self._thread_local, self.name)
+                return got
+            except AttributeError:
+                value = self.default()
+                self.set(value)
+                return value
+
+        def set(self, value: 'object') -> None:
+            setattr(self._thread_local, self.name, value)