Android Notifications communicate important information to users. NotificationChannel groups notifications by type for user control. Create channels with importance level: urgent, high, medium, low. NotificationCompat.Builder constructs notifications with required fields. Small icon appears in status bar, large icon in notification. Content title and text form the notification body. Notification actions allow user interaction without opening app. Expandable notifications reveal additional content on expansion. Inline reply actions accept text input within notification. Notification grouping organizes multiple notifications from same app. Progress indicators show ongoing task completion. MessagingStyle creates chat-style notification layouts. MediaStyle controls media playback notifications. Lock screen visibility controls notification content on lock screen. Importance levels affect interruption and display behavior. and sound patterns customize alert behavior. Notification badges show unread count on app icon. Time-sensitive notifications request urgent delivery. Direct reply action handles text input inline. Notification dismissal listeners track user engagement. Proper notification design balances timeliness with user respect.