The first supplementary volume in "The Chemistry of Functional Groups" series was published in 1976. This included thirteen chapters in the form of essay-reviews complementing the original main volumes in the series on C=C, C=O, C=N and N=N double bonds. As then, in the present second Supplement A2, several of the authors were asked to write chapters which give a unified and comparative treatment of several double-bonded functional groups together. This aim has been achieved and indeed more than half of the chapters in the book are such integrative ones, concentrated in the first part of the volume. Other chapters deal with special subjects which for various reasons have not been treated in the original volumes or in Supplement A. The literature coverage in most chapters is up to about the end of 1987 and in some cases even to the middle of 1988.