Clusterin, also known as Apolipoprotein J, Sulfated Glycoprotein 2 (SGP-2), TRPM-2, and SP-40,40, is a secreted multifunctional protein that binds a wide range of molecules and may function as a chaperone of misfolded extracellular proteins. It also participates in the control of cell proliferation, apoptosis, and carcinogenesis. Clusterin is predominantly expressed in adult testis, ovary, adrenal gland, liver, heart, and brain and in many epithelial tissues during embryonic development. It is secreted as a disulfide-linked heterodimer of alpha and beta chains and circulates as a component of high density lipoprotein (HDL) particles. Clusterin exerts tissue protective functions in atherosclerosis and Alzheimer’s disease by binding and neutralizing non-oxidatively modified LDL reduces cytotoxicity and beta-amyloid fibrils, respectively. Increased circulating levels of Clusterin enhance tumor aggressiveness by inhibiting apoptosis and by promoting epithelial to mesenchymal transition.