Lipases are esterases able to hydrolyze water-insoluble esters such as long-chain triglycerides. These enzymes also catalyze the formation of esters (esterification) and the exchange of ester bonds (transesterification) when present in nonaqueous media. Lipases display a high degree of specificity and enantioselectivity for esterification and transesterification reactions, and thus their potential uses in industry are very wide. These potential industrial applications have been an important driving force for lipase research during the last several years, and in particular for the study of lipases produced by microorganisms. Pseudomonas lipases are very interesting because they display special biochemical characteristics not common among the lipases produced by other microorganisms, such as their thermoresistance and activity at alkaline pHs. Recently, several Pseudomonas genes have been cloned and sequenced, and the regulation of their expression is beginning to be understood. The molecular genetic approach to the study of Pseudomonas lipases will permit the construction of recombinant strains with increased lipase productivity and will provide the opportunity to modify these enzymes to suit particular industrial applications.