ATP is a cotransmitter with classical transmitters in most nerves in the peripheral nervous system and central nervous system, although the proportions vary between species and tissues and in different developmental, physiological and pathophysiological conditions. ATP is released together with noradrenaline and neuropeptide Y from sympathetic nerves. It is released as a cotransmitter with acetylcholine from parasympathetic nerves supplying the bladder, developing skeletal neuromuscular junctions and some neurons in the brain. It is also released with nitric oxide and vasoactive intestinal polypeptide from non-adrenergic inhibitory enteric nerves, with glutamate from primary afferent sensory nerves and in the hypothalamus, and with dopamine and 5-hydroxytryptamine from some neurons in the central nervous system. Cotransmission offers subtle, local variations in neurotransmission and neuromodulation mechanisms.