The tumor necrosis factor (TNF) superfamily member TNF-like weak inducer of apoptosis (TWEAK) was initially described in a 1997 publication co-authored by investigators from the biotechnology company Biogen (now Biogen-Idec) and the University of Geneva. Four years later, researchers at the biotechnology company Immunex (now part of Amgen) reported the cloning and characterization of the human TWEAK receptor. A sequence database search revealed that the predicted TWEAK receptor amino acid sequence was identical to that of fibroblast growth factor-inducible 14 (Fn14), a small transmembrane protein described one year earlier in a publication from investigators at the American Red Cross Holland Laboratory. Recent studies have revealed that the TWEAK-Fn14 ligand-receptor pair likely plays an important role in a variety of cellular processes and in the pathogenesis of several human diseases, including atherosclerosis, stroke, rheumatoid arthritis and cancer. In this paper, we first summarize the general properties of these two proteins and then review the available data implicating TWEAK and Fn14 in multiple aspects of tumor biology.