Publisher Summary This chapter describes the crystallization of different pancreatic lipases and of their complexes with colipases and inhibitors. It analyzes their crystal packing in light of the crystallization experiments. Colipases are homologous proteins, which have the capability of cross activating pancreatic lipases from different organisms. The chapter uses this characteristic to obtain well-diffracting crystals of a heterologous complex between human pancreatic lipase and porcine (pro)colipase. A first form of a binary lipase-colipase complex had the active site covered by a lid, as found for the pancreatic lipase alone. When crystallized in the presence of a surfactant mixture including a phospholipid or of a Cll alkyl phosphonate, the ternary complex lipase-colipase-inhibitor was found to exhibit large conformational changes. Although the amino acid sequence is highly homologous to that of other known pancreatic lipases, this enzyme possesses a large deletion of 18 residues in the lid domain and has been shown to differ kinetically from the classic mammalian pancreatic lipases through the following: (1) no interfacial activation, (2) no effect of colipase, and (3) unusually high phospholipase A1 activity associated with a classic lipase activity.