Fyn is a 59 kDa member of the Src family of tyrosine kinases. The protein is synthesized and N-myristoylated on cytosolic polysomes and then rapidly targeted to the plasma membrane, where it is palmitoylated. Dually acylated Fyn clusters in caveolae-like membrane microdomains, and can interact with a variety of other signaling molecules. Fyn's biological functions are diverse, and include signaling via the T cell receptor, regulation of brain function, as well as adhesion mediated signaling. Alteration of the levels of Fyn in appropriate target tissues may lead to better treatments for alcoholism and autoimmune disease.