During the past decade we have witnessed a vast expansion in our knowl edge of lipid metabolism, especially for mammalian tissues. One obvious conclusion arising from these studies is that no single overall scheme of lipid metabolism can be classed as distinctly characteristic of all mamma lian organs. Although certain synthetic and degradative lipid pathways are similar in a variety of organs, I have been impressed by the notable exceptions. I was motivated to organize this work on Lipid Metabolism in Mammals because of the lack of a single reference source containing a comparative organ approach to lipid metabolism in mammals that empha sizes the uniqueness of pathways in the various organs of the body. Because of the escalation in lipid research, I also feel strongly that there is an urgent need for an updated concise account of this field. The group of authors for the chapters in the two volumes of Lipid Metabolism in Mammals were selected for their expertise and personal experience with the lipid metabolism of the organs or blood constituents that are the subjects of the chapters. Sufficient leeway has been given each author to approach the subject matter from a personal viewpoint. How ever, the overall direction of each chapter has been slanted to emphasize the similarities and differences in lipid metabolism among organ systems. The introductory chapter on general pathways provides a convenient refer ence to illustrations of specific reaction sequences that are well established and that occur in a number of organs.