1.Driven by externally generated events where the timing of the event is outside the control of the sub-systems which process the event
2.Two principal event-driven models
-Broadcast models. An event is broadcast to all sub- systems. Any sub-system which can handle the event may do so
-Interrupt-driven models. Used in real-time systems where interrupts are detected by an interrupt handler and passed to some other component for processing
3.Other event driven models include spreadsheets and production systems