Android applications can send or receive messages. Messages can be system-related events or custom ones defined by us. Interested parties are registered for certain messages by defining a proper intent filter and broadcast receiver. When a message is broadcast, all interested parties are notified. It is important to note that once you subscribe for broadcast messages (especially from the Activity class), you must unsubscribe at some point. When can we use broadcast messages? We use broadcast messages when we need a messaging system across our application. For example, imagine you started a long running process in the background. At some point, you want to notify multiple contexts about processing results. Broadcast messages are a perfect solution for this.