The arrestins are a family of proteins that are important for regulating signal transduction within cells. Arrestins are part of a conserved two step mechanism for regulating the activity of G-protein coupled receptors (GPCRs). In response to a stimulus, GPCRs activate a heterotrimeric G protein. In order to turn off this response, or adapt to a constant stimulus, activated receptors need to be silenced. The first step is phosphorylation by a class of serine/threonine kinases called G protein coupled receptor kinases (GRKs). This phosphorylation specifically marks the activated receptor for arrestin binding. Once arrestin is bound to the receptor it is unable to signal further. Recent research continues to expand the known actions of arrestins, which can bind to other classes of receptors and can directly activate signaling pathways on their own. Different arrestins (visual arrestin (or Arrestin 1), beta-arrestin 1 (or Arrestin 2) and beta-arrestin 2 (or Arrestin 3) can reduce the activity of their target GPCRs in several different ways.