Flies escape danger by jumping into the air and flying away. The giant fibre system (GFS) is the neural circuit that mediates this simple behavioural response to visual stimuli. The sensory signal is received by the giant fibre and relayed to the leg and wing muscle motorneurons. Many of the neurons in the Drosophila GFS are uniquely identifiable and amenable to cell biological, electrophysiological and genetic studies. Here we review the anatomy and development of this system and highlight its utility for studying many aspects of nervous system biology ranging from neural development and synaptic plasticity to the aetiology of neural disorder.