Fas Apoptosis Inhibitory Molecule (FAIM) is an anti-apoptotic protein that is up-regulated in B cell receptor (BCR)-activated B cells and confers upon them resistance to Fas-mediated cell death. Faim has two alternatively spliced isoforms, with the short isoform ubiquitously expressed in various tissues and the long isoform mainly found in the nervous tissues. FAIM is evolutionarily conserved but does not share any significant primary sequence homology with any known protein. The function of FAIM has been extensively studied in the past 20 years, with its primary role being ascribed to be anti-apoptotic. In addition, several other functions of FAIM were also discovered in different physiological and pathological conditions, such as cell growth, metabolism, Alzheimer's disease and tumorigenesis. However, the detailed molecular mechanisms underlying FAIM's role in these conditions remain unknown. In this review, we summarize comprehensively the functions of FAIM in these different contexts and discuss its potential as a diagnostic, prognostic or therapeutic target.