Abstract The sections in this article are: Pathways of De Novo Fatty Acid Biosynthesis and Lipolysis Regulation in the Pathways for Lipogenesis and Lipolysis Cellular Sites of Lipogenesis and Lipolysis Isolated Cell Models for the Study of Lipogenesis and Lipolysis Establishing Insulin and Glucagon as Regulators of Lipogenesis and Lipolysis Molecular Mechanisms Involved in the Regulation of Lipogenesis and Lipolysis Criteria for Evaluating Putative Regulatory Mechanisms Regulated Steps Summary