diff --git a/timelapse/__main__.py b/timelapse/__main__.py
index a6dc7ae..056d083 100644
--- a/timelapse/__main__.py
+++ b/timelapse/__main__.py
@@ -11,35 +11,35 @@
 from Foundation import NSUserDefaults
 
 
-def dark_mode():
+def dark_mode() -> bool:
     return NSUserDefaults.standardUserDefaults().stringForKey_('AppleInterfaceStyle') == "Dark"
 
 
 # Configuration
-start_recording = False  # Start recording on launch
-encode = True  # Create video after recording
-screenshot_interval = 1.5  # Number of seconds between screenshots
-dir_base = os.path.expanduser("~")  # Base directory
-dir_app = "timelapse"  # Output directory
-dir_pictures = "Pictures"  # Place for pictures in filesystem
-dir_movies = "Movies"  # Place for movies in filesystem
-dir_resources = "./resources/"
+start_recording: bool = False  # Start recording on launch
+encode: bool = True  # Create video after recording
+screenshot_interval: float = 1.5  # Number of seconds between screenshots
+dir_base: str = os.path.expanduser("~")  # Base directory
+dir_app: str = "timelapse"  # Output directory
+dir_pictures: str = "Pictures"  # Place for pictures in filesystem
+dir_movies: str = "Movies"  # Place for movies in filesystem
+dir_resources: str = "./resources/"
 if dark_mode():
     dir_resources += "white"
 else:
     dir_resources += "black"
 
-subdir_suffix = "Session-" + time.strftime("%Y%m%d")  # Name of subdirectory
-image_recording = "record.gif"  # App icon recording
-image_idle = "stop.gif"  # App icon idle
-create_session_subdir = True  # New screenshot directory for each session
-create_movies = True  # Create movies from screenshots after recording
+subdir_suffix: str = "Session-" + time.strftime("%Y%m%d")  # Name of subdirectory
+image_recording: str = "record.gif"  # App icon recording
+image_idle: str = "stop.gif"  # App icon idle
+create_session_subdir: str = True  # New screenshot directory for each session
+create_movies: bool = True  # Create movies from screenshots after recording
 # Menu item text when recorder is running
-text_recorder_running = "Stop recording"
-text_recorder_idle = "Start recording"  # Menu item text when recorder is idle
+text_recorder_running: str = "Stop recording"
+text_recorder_idle: str = "Start recording"  # Menu item text when recorder is idle
 # Tooltip of menu icon when not recording
-tooltip_idle = "Timelapse screen recorder"
-tooltip_running = "Recording | " + tooltip_idle  # Tooltip when recording
+tooltip_idle: str = "Timelapse screen recorder"
+tooltip_running: str = "Recording | " + tooltip_idle  # Tooltip when recording
 
 
 ###############
@@ -47,19 +47,19 @@ def dark_mode():
 class Timelapse(NSObject):
     """ Creates a timelapse video """
 
-    def applicationDidFinishLaunching_(self, notification):
+    def applicationDidFinishLaunching_(self, notification) -> None:
         self.check_dependencies()
 
         # Initialize recording
-        self.recording = start_recording
+        self.recording: bool = start_recording
         self.recorder = None
 
         # Set correct output paths
-        self.recorder_output_basedir = os.path.join(
+        self.recorder_output_basedir: str = os.path.join(
             dir_base, dir_pictures, dir_app)
-        self.encoder_output_basedir = os.path.join(dir_base, dir_movies)
+        self.encoder_output_basedir: str = os.path.join(dir_base, dir_movies)
 
-        self.image_dir = self.create_dir(self.recorder_output_basedir)
+        self.image_dir: str = self.create_dir(self.recorder_output_basedir)
 
         # Create a reference to the statusbar (menubar)
         self.statusbar = NSStatusBar.systemStatusBar()
@@ -77,13 +77,13 @@ def applicationDidFinishLaunching_(self, notification):
         self.loadIcons()
         self.setStatus()
 
-    def loadIcons(self):
+    def loadIcons(self) -> None:
         self.icon_recording = NSImage.alloc().initWithContentsOfFile_(
             os.path.join(dir_resources, image_recording))
         self.icon_idle = NSImage.alloc().initWithContentsOfFile_(
             os.path.join(dir_resources, image_idle))
 
-    def setStatus(self):
+    def setStatus(self) -> None:
         """ Sets the image and menu text according to recording status """
         if self.recording:
             self.statusitem.setImage_(self.icon_recording)
@@ -94,7 +94,7 @@ def setStatus(self):
             self.recordButton.setTitle_(text_recorder_idle)
             self.statusitem.setToolTip_(tooltip_idle)
 
-    def createMenu(self):
+    def createMenu(self) -> menu:
         """ Status bar menu """
         menu = NSMenu.alloc().init()
         # Bind record event
@@ -107,7 +107,7 @@ def createMenu(self):
         menu.addItem_(menuitem)
         return menu
 
-    def startStopRecording_(self, notification):
+    def startStopRecording_(self, notification) -> None:
         if self.recording:
             self.recorder.join(timeout=screenshot_interval*2)
             # Create timelapse after recording?
@@ -119,18 +119,18 @@ def startStopRecording_(self, notification):
             notify("Timelapse started", "The recording has started")
             self.recorder = Recorder(self.image_dir, screenshot_interval)
             self.recorder.start()
-        self.recording = not self.recording
+        self.recording: bool = not self.recording
         self.setStatus()
 
     @objc.python_method
-    def create_dir(self, base_dir):
+    def create_dir(self, base_dir: str) -> str:
         """ Creates a specified directory and the path to it if necessary """
         if create_session_subdir:
             # Create a new subdirectory
-            output_dir = os.path.join(base_dir, self.get_sub_dir(base_dir))
+            output_dir: str = os.path.join(base_dir, self.get_sub_dir(base_dir))
         else:
             # Don't create a subdirectory. Use base directory for output
-            output_dir = base_dir
+            output_dir: str = base_dir
         # Create path if it doesn't exist
         try:
             print(f"Output directory: {output_dir}")
@@ -144,20 +144,20 @@ def create_dir(self, base_dir):
         return output_dir
 
     @objc.python_method
-    def get_sub_dir(self, base_dir):
+    def get_sub_dir(self, base_dir: str) -> str:
         """ Returns the next nonexistend subdirectory to base_dir """
-        subdir_base = os.path.join(base_dir, subdir_suffix)
+        subdir_base: str = os.path.join(base_dir, subdir_suffix)
         # Check if we can use subdir without any session id
-        subdir = subdir_base
+        subdir: str = subdir_base
         # Use a session id only if subdir already exists
-        session_number = 0
+        session_number: int = 0
         while os.path.exists(subdir):
             # We can't use subdir. Create directory with session id
             session_number += 1
-            subdir = subdir_base + "-" + str(session_number)
+            subdir: str = subdir_base + "-" + str(session_number)
         return subdir
 
-    def check_dependencies(self):
+    def check_dependencies(self) -> None:
         try:
             subprocess.run(['ffmpeg'], check=True,
                            capture_output=True, timeout=10.0)
diff --git a/timelapse/encoder.py b/timelapse/encoder.py
index ddc480d..b78bbed 100644
--- a/timelapse/encoder.py
+++ b/timelapse/encoder.py
@@ -6,6 +6,7 @@
 import fnmatch
 import shutil
 from notify import notify  # Shows notifications/alerts
+from typing import List
 
 not_found_msg = """
 The ffmpeg command was not found;
@@ -18,22 +19,22 @@
 class Encoder(Thread):
     """Create a video file from images"""
 
-    def __init__(self, input_dir, output_dir):
+    def __init__(self, input_dir: str, output_dir: str) -> None:
         # Initialize the thread
         Thread.__init__(self)
 
         # Set config options
-        self.input = f"{input_dir}/%d.png"
-        timestamp = datetime.now().strftime("%Y-%m-%d-%H-%M-%S")
-        self.output = f"{output_dir}/timelapse-{timestamp}.mov"
+        self.input: str = f"{input_dir}/%d.png"
+        timestamp: str = datetime.now().strftime("%Y-%m-%d-%H-%M-%S")
+        self.output: str = f"{output_dir}/timelapse-{timestamp}.mov"
 
         print("Encoder started")
 
-    def join(self, timeout=None):
+    def join(self, timeout=None) -> None:
         """ Hard shutdown """
         Thread.join(self)
 
-    def run(self):
+    def run(self) -> None:
         """
         Now that we have screenshots of the user's desktop, we will stitch them
         together using `ffmpeg` to create a movie.  Each image will become
@@ -41,7 +42,7 @@ def run(self):
         """
         # Call ffmpeg with settings compatible with QuickTime.
         # https://superuser.com/a/820137
-        command = ["/usr/local/bin/ffmpeg", "-y",
+        command: List[str]= ["/usr/local/bin/ffmpeg", "-y",
                    "-framerate", "30",
                    "-i", self.input,
                    "-vf", "format=yuv420p",
diff --git a/timelapse/notify.py b/timelapse/notify.py
index 12d0289..89b6275 100644
--- a/timelapse/notify.py
+++ b/timelapse/notify.py
@@ -1,7 +1,7 @@
 import os
 
 
-def notify(title, text):
+def notify(title: str, text: str) -> int:
     os.system("""
               osascript -e 'display notification "{}" with title "{}"'
               """.format(text, title))
diff --git a/timelapse/recorder.py b/timelapse/recorder.py
index cc55d0d..ce221ef 100644
--- a/timelapse/recorder.py
+++ b/timelapse/recorder.py
@@ -6,7 +6,7 @@
 from AppKit import NSEvent, NSScreen, NSMouseInRect
 
 
-def get_screen_with_mouse_index():
+def get_screen_with_mouse_index() ->int:
     mouseLocation = NSEvent.mouseLocation()
     screens = NSScreen.screens()
     for i, screen in enumerate(screens):
@@ -20,7 +20,7 @@ class Recorder(Process):
     Takes a screenshot every 'interval' seconds and saves it into output_dir or a subdirectory thereof.
     """
 
-    def __init__(self, output_dir, interval=4):
+    def __init__(self, output_dir: str, interval: int=4) -> None:
         # Initialize the thread
         Process.__init__(self)
 
@@ -29,15 +29,15 @@ def __init__(self, output_dir, interval=4):
         self._stopped = Event()
 
         # Set config options
-        self.output_dir = output_dir
-        self.interval = interval
-        self.format = "png"
+        self.output_dir: str = output_dir
+        self.interval: int = interval
+        self.format: str = "png"
 
         # Number of screenshots taken
-        self.screenshot_counter = 0
+        self.screenshot_counter: int = 0
         print("Recorder started")
 
-    def join(self, timeout=None):
+    def join(self, timeout=None) -> None:
         """ Stop recording """
         self._stop.set()
         self._stopped.wait()
@@ -45,7 +45,7 @@ def join(self, timeout=None):
               self.get_recording_time() + ".")
         Process.join(self, timeout=timeout)
 
-    def run(self):
+    def run(self) -> None:
         """ Periodically take a screenshots of the screen """
         while not self._stop.is_set():
             self.screenshot()
@@ -53,18 +53,18 @@ def run(self):
 
         self._stopped.set()
 
-    def get_recording_time(self):
+    def get_recording_time(self) ->str:
         return str(self.screenshot_counter * self.interval) + " seconds"
 
-    def get_filename(self):
+    def get_filename(self) ->str:
         """ Call screencapture for mac screenshot """
-        filename = os.path.join(
+        filename: str = os.path.join(
             self.output_dir, f"{self.screenshot_counter}.{self.format}")
         return filename
 
-    def screenshot(self):
+    def screenshot(self) -> None:
         """ This method uses Mac OSX screencapture from the commandline """
-        filename = self.get_filename()
+        filename: str = self.get_filename()
         subprocess.run(
             ['screencapture', '-S', '-o', '-x', '-D',
                 str(get_screen_with_mouse_index() + 1), '-t', self.format, filename],