Message to system to start a component
Can return a result
Service
Allows two processes to communicate
Represents an Event
Can interact with a database
Responds to events
May contain Fragments
ContentProvider
Acts as a gateway to other components
Activity
Maintains application data
Does work in the background
Does work for external applications
Handles user input
Intent
Starts a broadcast recevier
Displays a user interface
Starts an Activity
Receives intents that have been broadcast
BroadcastReceiver
Starts a service
Goes on the back stack
