GABA(B) receptors are a distinct subclass of receptors for the major inhibitory transmitter 4-aminobutanoic acid (GABA) that mediate depression of synaptic transmission and contribute to the inhibition controlling neuronal excitability. The development of specific agonists and antagonists for these receptors has led to a better understanding of their physiology and pharmacology, highlighting their diverse coupling to different intracellular effecters through G(i)/G(o) proteins. This review emphasises our current knowledge of the neurophysiology and neurochemistry of GABA(B) receptors, including their heterogeneity, as well as the therapeutic potential of drugs acting at these sites.