In the course of the light-evoked ERG a-, b-, and c-waves represent a functional equivalent of the receptor layer, the postreceptor elements, and the pigment epithelium. More sophisticated recording techniques reveal additional components: an early receptor potential (ERP, which is a signal from the receptor outer segments), photopic and scotopic responses (or components expressing cone and rod function), and the oscillatory potentials (OP, originating in the inner retinal layers and depending strongly on the vascular status). With pattern-reversal stimuli a signal can be evoked (P-ERG), which is mainly determined by ganglion cell function. The electro-oculogram (EOG) is a special signal from the pigment epithelium that is independent of the ERG. Analysis of these different components solves important practical problems in establishing a clinical differential diagnosis.