Fn14, the TWEAK receptor, is a recently identified member of the TNF receptor superfamily and is expressed on smooth muscle cells and endothelial cells. It is a weak inducer of apoptosis and promotes angiogenesis. Fn14 is a type 1 membrane protein. It associates with TRAF1 and TRAF2, and may modulate cellular adhesion to matrix proteins. Fn14 is highly expressed in heart, placenta and kidney, and moderately expressed in lung, skeletal muscle and pancreas. It is the smallest member of the TNF receptor (TNFR) superfamily described to date, and signals via recruitment of several different TNFR-associated factors.