MIF was discovered in the 1960’s as a T-lymphocyte product that inhibits the random migration of macrophages during delayed-type hypersensitivity responses. This cytokine is a single, non-glycosylated, 115 amino acid polypeptide that has a β-α-β motif. It is known that MIF induces inflammatory cytokines, nitric oxide and superoxide anions, and regulates macrophage and lymphocyte proliferation. The immunoregulatory activities of MIF are based upon transcriptional regulation of inflammatory gene products, modulation of cell proliferation and cell cycle inhibition of p53-mediated apoptosis, and a number of metabolic effects. MIF also demonstrates broad regulatory properties and is considered to be a critical mediator of multiple disorders, including inflammatory and autoimmune diseases such as rheumatoid arthritis, glomerulonephritis, diabetes, atherosclerosis, sepsis, asthma, and acute respiratory distress syndrome. Furthermore, studies have highlighted the role of MIF in tumorigenesis. Human cancer tissues, including skin, brain, breast, colon, prostate, and lung-derived tumors, overexpress MIF: MIF levels correlated with tumor aggressiveness and metastatic potential. Therefore, MIF is considered a potential therapeutic target for treating inflammatory diseases and neoplasia. In addition to its physiologic and pathophysiologic activities, MIF is known to act as a tautomerase and has a catalytically active N-terminal proline that is invariant in structurally homologous bacterial isomerases. Although the relationship between the catalytic activity and biological function of MIF is not yet fully understood, targeting MIF tautomerase activity using small-molecule inhibitors has emerged as an attractive strategy for inhibiting MIF proinflammatory activity and attenuating its biological activity in vitro and in vivo. Human and mouse MIF share a 90% homology.