The explosive growth of organoselenium chemistry over the past 12 years can be attributed to the specific properties of organic selenium molecules, which fit the requirements of modern organic synthesis. Most of them are well adapted to chemo-, regio- and stereo-selectivities. In addition, they can be used in mild experimental conditions which are compatible with the stability of both substrates and products in the preparation of unsaturated and functional complex molecules, especially in the field of natural products. This book describes and illustrates different synthetic routes to organic structures using selenium reagents or intermediates. The approach emphasizes that such transformations are simple, efficient and often carried out at room temperature. The scope ranges from the preparation of both inorganic and organic selenium reagents, through descriptions of structure, toxicity, biological aspects and nuclear magnetic resonance, to applications of specific selenium compounds in various syntheses including natural products and biologically active compounds.