A lipase is an enzyme that catalyzes the hydrolysis of fats (lipids). Lipases perform essential roles in the digestion, transport and processing of dietary lipids (e.g. triglycerides, fats, oils) in most, if not all, living organisms. Genes encoding lipases are even present in certain viruses.

Although a diverse array of genetically distinct lipase enzymes are found in nature; and, they represent several types of protein folds and catalytic mechanisms, most of them are built on an alpha/beta hydrolase fold and employ a chymotrypsin-like hydrolysis mechanism using a catalytic triad consisting of a serine nucleophile, a histidine base, and an acid residue (usually aspartic acid). Lipase can also assist in the breakdown of fats into lipids in those undergoing pancreatic enzyme replacement therapy(PERT).