Scientific reviews are now of two complementary types: short, very up-to-date articles, as are found in the Trends series, and the more traditional longer re- views, which are more comprehensive but take longer to publish. The Subcellu- lar Biochemistry series belongs to the latter category where a number of reviews on a broad topic are collected together in the one volume. It has been the aim of this volume to summarize the present state of knowledge of membrane assembly. It is appreciated that some relevant topics have not been included, and an editor’s selection is restricted by the many calls on potential authors who are unable to meet all requests made to them. The absence of a discussion of the roles of lipids is, " however, a reflection of the fact that a recent volume in this series, edited by Dr. H. 1. Hilderson, has been devoted to this subject (Vol. 16, Intracellular Transfer of Lipid Molecules), and readers are recommended to this source.