Dipeptidyl peptidase-4 (DPP-4), originally identified in 1966 as a dipeptide naphthylamidase hydrolyzing glycyl-prolyl-beta-naphthylamide, is a membrane-associated peptidase that selectively cleaves the N-terminal penultimate proline or alanine amino acids. The most common substrates of DPP-4 include glucagon-like peptide-1 (GLP-1), glucagon-like peptide-2 (GLP-2), peptide YY, neuropeptide, chemokine ligand 12/stromal-derived factor-1 (CXCL12/SDF-1) and substance P. DPP-4, as a type II cell surface protein and a soluble form, has been found to be widely distributed in organs (such as the bone marrow, the lung, spleen, liver, pancreas, kidney and intestines) and body fluids (such as serum/plasma, cerebrospinal fluid, synovial fluid and semen). Besides its peptidase activity, DPP-4 has been found to be associated with immune stimulation, extracellular matrix degradation, lipid accumulation and resistance to anticancer agents.