Lipoprotein lipase and it's cofactor, apolipoprotein C-ll, are complex proteins which contain multiple functional domains essential for normal triglyceride hydrolysis. Recent studies have provided new insights into the various sites involved in catalysis, heparin and lipid binding, and enzyme-cofactor interaction resulting in an increased understanding of the structure-function relationships of both proteins, as well as of the potential role that defects in lipoprotein lipase and apolipoprotein C-II may play in the development of various dyslipidemic disorders.