Organoselenium compounds are very versatile radical precursors which are widely used. Due to their stability and ease of preparation, they offer unique advantages over organic halides as radical precursors. They can be utilized in tin mediated radical reactions as well as in group transfer reactions for the formation of carbon-carbon bonds and carbon-heteroatom bonds. Selenols and diselenides have found applications as reducing agents and radical traps, respectively. A survey of these different reaction types will be given. Information about new reactions based on electron and photoelectron transfers will also be provided.