We describe molecular and physiological properties of human lipoprotein lipase (LPL) based on recent advanced knowledges. Human LPL is a lipolytic glycoprotein enzyme synthesized by extrahepatic tissues, mainly adipocytes, and its gene is located on chromosome 8p22 with 10 exons that encode mRNAs of 3.4 kb and 3.8 kb. Clinical and biochemical studies indicate that LPL plays a key role in hydrolyzing the triglycerides of chylomicrons and very low density lipoproteins (VLDL) at the first step in their metabolism. LPL is believed to be taken on a functionally active form at the site of capillary endothelial cell surface following a series of three major processes: (1) the synthesis and secretion of LPL by adipocytes, (2) the transport of LPL from adipocytes to the capillary endothelium, and (3) the binding of LPL to heparan sulfate proteoglycan chains which are localized in the plasma membrane of the endothelium. LPL is released into the circulation after intravenous injection of heparin, and LPL is recovered in postheparin plasma (PHP). LPL purified from human PHP is catalytically active in a monomeric form, and its molecular size is 61 k dalton in good agreement with mature LPL size estimated by cDNA of LPL.