This review has described the many behavioural and arousal-related influences on breathing and the extent of these influences in humans. The chief examples have included the effect on breathing of altered mental activity, wakefulness and sleep, and learned respiratory responses. Determining the precise neurological mechanisms underlying these effects represents a difficult challenge to respiratory physiologists who seek to understand the respiratory control system of awake behaving humans. Nevertheless, insight into the various forebrain and brainstem inputs to respiratory muscles has been gained by studies of breathing during particular behaviours (when either voluntary or reflex breathing predominates) or in particular neurological patients (in whom either voluntary or reflex breathing is defective). With developments in brain imaging techniques, such as functional magnetic resonance imaging, it may soon be possible to determine more precisely the various anatomical sources and timing of the motor commands to breathe during different behaviours, states of arousal and sleep.