New reactivities of silylboranes are described with their applications to organic synthesis. The silylboranes add to unsaturated organic compounds such as alkynes, alkenes, 1,3-dienes, and allenes in the presence of nickel, palladium, and platinum catalysts. Reactions with isocyanide proceed in the absence of catalysts, giving 1,1-addition products. The silaborations proceed in highly regio-and stereoselective manners, leading to the formation of organic compounds bearing silyl and boryl groups. Silaborations accompanied by regioselective CÍC bond cleavage in three-membered rings take place in the reactions of methylenecyclopropane and vinylcyclopropane derivatives. Unsaturated organic molecules, e.g., 1,3-diene and aldehyde, undergo silaborative CÍC coupling reactions in the presence of transition-metal catalysts. Enantioselective silaboration of terminal allenes and silaborative CÍC cleavage of meso-methylenecyclopropanes have been achieved. Silaborations in which the stereochemical course, i.e., cis and trans stereoselectivities, is governed by the ligand have been established in platinum-catalyzed intramolecular silaborations of alkenes. Synthetic applications of the silaboration products through SuzukiÍMiyaura coupling, one-carbon homologation, oxidation, allylation, and Rhcatalyzed conjugate addition are also described. Synthesis of silylboranes, including those having heteroatom functional groups at the silicon atoms, is summarized.