Arrestins are cytosolic proteins involved in the termination of signaling by activated G protein-coupled receptors (GPCR). Four different arrestins are identified in mammals to date. Two of these are specific to retinal photoreceptor cells, while the other two (beta-arrestin 1 and 2) are ubiquitously expressed. Recently, several new regulatory functions of arrestins in such processes as receptor ubiquitination, signaling through kinases, and others have been discovered.