Clusterin (APO J, SGP-2, TRPM-2, SP-40, pADHC-9, CLJ, T64, GP III, XIP8) is a 75-80 kD disulfide-linked heterodimeric protein containing about 30% of N-linked carbohydrate rich in sialic acid but truncated forms targeted to the nucleus have also been identified. It is a conserved secreted glycoprotein expressed by a wide range of tissues and being implicated in many physiological processes, including e.g. lipid transportation, complement inhibition, tissue remodeling, membrane recycling, or clearence of cellular debris. It is nearly ubiqitously expressed in most mammalian tissues and can be found in plasma, milk, urine, cerebrospinal fluid and semen. Clusterin is able to bind and form complexes with numerous partners (immunoglobulins, lipids, heparin, bacteria, complement components, paraoxonase, beta amyloid, leptin etc.) and is expressed in many pathological and clinically relevant situations including cancer, organ regeneration, infection, Alzheimer disease, retinitis pigmentosa, myocardial infarction, renal tubular damage, autoimmunity and others. A genuine function of clusterin is still enigmatic.