Rod and cone photoreceptors transduce the absorption of a photon of light into an electrical response. Within the last decade, our understanding of photoreceptors has increased enormously, and this growth in understanding has resulted in large part from the application of new electrophysiological techniques to these cells. The biochemistry and physiology of phototransduction have been extensively reviewed elsewhere (Stryer, 1986 , 1988 ; Pugh and Cobbs, 1986 ; Pugh, 1987 ; Liebman et al., 1987 ; Hurley, 1987 ; Fain and Matthews, 1990 ; McNaughton, 1990 ; Pugh and Lamb, 1990 ); in this chapter, we concern ourselves with the electrophysiological techniques themselves.