diff --git a/.travis.yml b/.travis.yml
index 3e1c8869d8f..3d575c1d778 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -8,8 +8,13 @@ matrix:
       env: TOXENV=requirements
     - python: "3.5"
       env: TOXENV=lint
+    - python: "3.5"
+      env: TOXENV=typing
     - python: "3.5"
       env: TOXENV=py35
+  allow_failures:
+    - python: "3.5"
+      env: TOXENV=typing
 cache:
   directories:
     - $HOME/.cache/pip
diff --git a/homeassistant/__main__.py b/homeassistant/__main__.py
index d92c434d22b..fb1594d5b3f 100644
--- a/homeassistant/__main__.py
+++ b/homeassistant/__main__.py
@@ -8,6 +8,8 @@ import subprocess
 import sys
 import threading
 
+from typing import Optional, List
+
 from homeassistant.const import (
     __version__,
     EVENT_HOMEASSISTANT_START,
@@ -16,7 +18,7 @@ from homeassistant.const import (
 )
 
 
-def validate_python():
+def validate_python() -> None:
     """Validate we're running the right Python version."""
     major, minor = sys.version_info[:2]
     req_major, req_minor = REQUIRED_PYTHON_VER
@@ -27,7 +29,7 @@ def validate_python():
         sys.exit(1)
 
 
-def ensure_config_path(config_dir):
+def ensure_config_path(config_dir: str) -> None:
     """Validate the configuration directory."""
     import homeassistant.config as config_util
     lib_dir = os.path.join(config_dir, 'deps')
@@ -56,7 +58,7 @@ def ensure_config_path(config_dir):
             sys.exit(1)
 
 
-def ensure_config_file(config_dir):
+def ensure_config_file(config_dir: str) -> str:
     """Ensure configuration file exists."""
     import homeassistant.config as config_util
     config_path = config_util.ensure_config_exists(config_dir)
@@ -68,7 +70,7 @@ def ensure_config_file(config_dir):
     return config_path
 
 
-def get_arguments():
+def get_arguments() -> argparse.Namespace:
     """Get parsed passed in arguments."""
     import homeassistant.config as config_util
     parser = argparse.ArgumentParser(
@@ -125,12 +127,12 @@ def get_arguments():
 
     arguments = parser.parse_args()
     if os.name != "posix" or arguments.debug or arguments.runner:
-        arguments.daemon = False
+        setattr(arguments, 'daemon', False)
 
     return arguments
 
 
-def daemonize():
+def daemonize() -> None:
     """Move current process to daemon process."""
     # Create first fork
     pid = os.fork()
@@ -155,7 +157,7 @@ def daemonize():
     os.dup2(outfd.fileno(), sys.stderr.fileno())
 
 
-def check_pid(pid_file):
+def check_pid(pid_file: str) -> None:
     """Check that HA is not already running."""
     # Check pid file
     try:
@@ -177,7 +179,7 @@ def check_pid(pid_file):
     sys.exit(1)
 
 
-def write_pid(pid_file):
+def write_pid(pid_file: str) -> None:
     """Create a PID File."""
     pid = os.getpid()
     try:
@@ -187,7 +189,7 @@ def write_pid(pid_file):
         sys.exit(1)
 
 
-def closefds_osx(min_fd, max_fd):
+def closefds_osx(min_fd: int, max_fd: int) -> None:
     """Make sure file descriptors get closed when we restart.
 
     We cannot call close on guarded fds, and we cannot easily test which fds
@@ -205,7 +207,7 @@ def closefds_osx(min_fd, max_fd):
             pass
 
 
-def cmdline():
+def cmdline() -> List[str]:
     """Collect path and arguments to re-execute the current hass instance."""
     if sys.argv[0].endswith('/__main__.py'):
         modulepath = os.path.dirname(sys.argv[0])
@@ -213,16 +215,17 @@ def cmdline():
     return [sys.executable] + [arg for arg in sys.argv if arg != '--daemon']
 
 
-def setup_and_run_hass(config_dir, args):
+def setup_and_run_hass(config_dir: str,
+                       args: argparse.Namespace) -> Optional[int]:
     """Setup HASS and run."""
     from homeassistant import bootstrap
 
     # Run a simple daemon runner process on Windows to handle restarts
     if os.name == 'nt' and '--runner' not in sys.argv:
-        args = cmdline() + ['--runner']
+        nt_args = cmdline() + ['--runner']
         while True:
             try:
-                subprocess.check_call(args)
+                subprocess.check_call(nt_args)
                 sys.exit(0)
             except subprocess.CalledProcessError as exc:
                 if exc.returncode != RESTART_EXIT_CODE:
@@ -244,7 +247,7 @@ def setup_and_run_hass(config_dir, args):
             log_rotate_days=args.log_rotate_days)
 
     if hass is None:
-        return
+        return None
 
     if args.open_ui:
         def open_browser(event):
@@ -261,7 +264,7 @@ def setup_and_run_hass(config_dir, args):
     return exit_code
 
 
-def try_to_restart():
+def try_to_restart() -> None:
     """Attempt to clean up state and start a new homeassistant instance."""
     # Things should be mostly shut down already at this point, now just try
     # to clean up things that may have been left behind.
@@ -303,7 +306,7 @@ def try_to_restart():
     os.execv(args[0], args)
 
 
-def main():
+def main() -> int:
     """Start Home Assistant."""
     validate_python()
 
diff --git a/homeassistant/bootstrap.py b/homeassistant/bootstrap.py
index 8b3d3ee6f23..71e6b88e310 100644
--- a/homeassistant/bootstrap.py
+++ b/homeassistant/bootstrap.py
@@ -6,9 +6,11 @@ import os
 import sys
 from collections import defaultdict
 from threading import RLock
+from typing import Any, Optional, Dict
 
 import voluptuous as vol
 
+
 import homeassistant.components as core_components
 from homeassistant.components import group, persistent_notification
 import homeassistant.config as conf_util
@@ -202,9 +204,14 @@ def prepare_setup_platform(hass, config, domain, platform_name):
 
 
 # pylint: disable=too-many-branches, too-many-statements, too-many-arguments
-def from_config_dict(config, hass=None, config_dir=None, enable_log=True,
-                     verbose=False, skip_pip=False,
-                     log_rotate_days=None):
+def from_config_dict(config: Dict[str, Any],
+                     hass: Optional[core.HomeAssistant]=None,
+                     config_dir: Optional[str]=None,
+                     enable_log: bool=True,
+                     verbose: bool=False,
+                     skip_pip: bool=False,
+                     log_rotate_days: Any=None) \
+                     -> Optional[core.HomeAssistant]:
     """Try to configure Home Assistant from a config dict.
 
     Dynamically loads required components and its dependencies.
@@ -266,8 +273,11 @@ def from_config_dict(config, hass=None, config_dir=None, enable_log=True,
     return hass
 
 
-def from_config_file(config_path, hass=None, verbose=False, skip_pip=True,
-                     log_rotate_days=None):
+def from_config_file(config_path: str,
+                     hass: Optional[core.HomeAssistant]=None,
+                     verbose: bool=False,
+                     skip_pip: bool=True,
+                     log_rotate_days: Any=None):
     """Read the configuration file and try to start all the functionality.
 
     Will add functionality to 'hass' parameter if given,
diff --git a/homeassistant/config.py b/homeassistant/config.py
index bf0cbdba23b..2450453863f 100644
--- a/homeassistant/config.py
+++ b/homeassistant/config.py
@@ -73,14 +73,14 @@ CORE_CONFIG_SCHEMA = vol.Schema({
 })
 
 
-def get_default_config_dir():
+def get_default_config_dir() -> str:
     """Put together the default configuration directory based on OS."""
     data_dir = os.getenv('APPDATA') if os.name == "nt" \
         else os.path.expanduser('~')
     return os.path.join(data_dir, CONFIG_DIR_NAME)
 
 
-def ensure_config_exists(config_dir, detect_location=True):
+def ensure_config_exists(config_dir: str, detect_location: bool=True) -> str:
     """Ensure a config file exists in given configuration directory.
 
     Creating a default one if needed.
diff --git a/homeassistant/core.py b/homeassistant/core.py
index 82ec20c82f9..aec9cce5612 100644
--- a/homeassistant/core.py
+++ b/homeassistant/core.py
@@ -57,7 +57,7 @@ class CoreState(enum.Enum):
     running = "RUNNING"
     stopping = "STOPPING"
 
-    def __str__(self):
+    def __str__(self) -> str:
         """Return the event."""
         return self.value
 
@@ -75,11 +75,11 @@ class HomeAssistant(object):
         self.state = CoreState.not_running
 
     @property
-    def is_running(self):
+    def is_running(self) -> bool:
         """Return if Home Assistant is running."""
         return self.state == CoreState.running
 
-    def start(self):
+    def start(self) -> None:
         """Start home assistant."""
         _LOGGER.info(
             "Starting Home Assistant (%d threads)", self.pool.worker_count)
@@ -90,7 +90,7 @@ class HomeAssistant(object):
         self.pool.block_till_done()
         self.state = CoreState.running
 
-    def block_till_stopped(self):
+    def block_till_stopped(self) -> int:
         """Register service homeassistant/stop and will block until called."""
         request_shutdown = threading.Event()
         request_restart = threading.Event()
@@ -132,7 +132,7 @@ class HomeAssistant(object):
 
         return RESTART_EXIT_CODE if request_restart.isSet() else 0
 
-    def stop(self):
+    def stop(self) -> None:
         """Stop Home Assistant and shuts down all threads."""
         _LOGGER.info("Stopping")
         self.state = CoreState.stopping
@@ -290,7 +290,7 @@ class EventBus(object):
             # available to execute this listener it might occur that the
             # listener gets lined up twice to be executed.
             # This will make sure the second time it does nothing.
-            onetime_listener.run = True
+            setattr(onetime_listener, 'run', True)
 
             self.remove_listener(event_type, onetime_listener)
 
diff --git a/homeassistant/scripts/__init__.py b/homeassistant/scripts/__init__.py
index a0e16efc7d1..87771045b66 100644
--- a/homeassistant/scripts/__init__.py
+++ b/homeassistant/scripts/__init__.py
@@ -3,7 +3,7 @@ import importlib
 import os
 
 
-def run(args):
+def run(args: str) -> int:
     """Run a script."""
     scripts = [fil[:-3] for fil in os.listdir(os.path.dirname(__file__))
                if fil.endswith('.py') and fil != '__init__.py']
@@ -19,4 +19,4 @@ def run(args):
         return 1
 
     script = importlib.import_module('homeassistant.scripts.' + args[0])
-    return script.run(args[1:])
+    return script.run(args[1:])  # type: ignore
diff --git a/requirements_all.txt b/requirements_all.txt
index e6f1c1530bf..50c8e4bfca9 100644
--- a/requirements_all.txt
+++ b/requirements_all.txt
@@ -5,6 +5,7 @@ pytz>=2016.6.1
 pip>=7.0.0
 jinja2>=2.8
 voluptuous==0.8.9
+typing>=3,<4
 sqlalchemy==1.0.14
 
 # homeassistant.components.isy994
diff --git a/requirements_test.txt b/requirements_test.txt
index 649859f2506..a1e799b7cc5 100644
--- a/requirements_test.txt
+++ b/requirements_test.txt
@@ -7,3 +7,4 @@ pytest-timeout>=1.0.0
 pytest-capturelog>=0.7
 pydocstyle>=1.0.0
 requests_mock>=1.0
+mypy-lang>=0.4
diff --git a/setup.py b/setup.py
index 32d24b56003..3d2d4b4e2c2 100755
--- a/setup.py
+++ b/setup.py
@@ -17,6 +17,7 @@ REQUIRES = [
     'pip>=7.0.0',
     'jinja2>=2.8',
     'voluptuous==0.8.9',
+    'typing>=3,<4',
     'sqlalchemy==1.0.14',
 ]
 
diff --git a/tox.ini b/tox.ini
index bc5acbd71cc..a7fdf3bcb49 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py34, py35, lint, requirements
+envlist = py34, py35, lint, requirements, typing
 skip_missing_interpreters = True
 
 [testenv]
@@ -29,3 +29,8 @@ basepython = python3
 deps =
 commands =
          python script/gen_requirements_all.py validate
+
+[testenv:typing]
+basepython = python3
+commands =
+         mypy --silent-imports homeassistant