During the last fifteen years organoselenium chemistry underwent a spectacular mutation: from an exotic area of science practised by a few specialists it became a relatively well mastered and widely used methodology of synthetic organic chemistry. The key to this success is that a fair number of selenium based reagents and reactions have been discovered, which are able to perform specific transformations selectively and often under very mild conditions. The aim of this volume is to present the different selenium containing reagents now available to chemists, to mention the scope as well as the limitations of their reactions, and to compare those which possess similar reactivities. The authors present the reagents in the order of increasing oxidation level around the selenium atom.