Our current understanding about how the signals that are generated in rods and cones are transmitted through the retina to the optic nerve has advanced rapidly in recent years. The basic principles were established from work using intracellular microelectrodes. More recent advances derive from using patch electrodes, which have the advantage of controlling the intracellular biochemistry and permitting more direct analysis of the properties of membrane ionic channels. Coupled with other novel techniques, such as imaging single neurons in retinal slices of both lower vertebrates and mammals, the advances that have been made in recent years have been striking. Furthermore, molecular biological approaches using mutant mice that lack specific receptors or channels have demonstrated the roles these play in signal transduction.