Due to various special physiological features and a genome that greatly differs in structure, gene content and organization from other yeasts, Y. lipolytica is widely used as a host system. With its characteristics, such as the ability to grow on lipids or grease, to accumulate oil and the high capacity for secretion of proteases and lipases, the yeast is of great interest for biotechnological applications. The main topics covered in this Microbiology Monograph are: expression and secretion of heterologous proteins; acid and alkaline extracellular proteases; genetics, production, biochemical characterization and biotechnological application of lipases; production and secretion of several organic acids and flagrances; as well as the functional expression of P450 systems and its use in steroid biotransformation.