Abstract 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 C–C 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 C–C coupling reactions in the presence of transition-metal catalysts. Enantioselective silaboration of terminal allenes and silaborative C–C 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 Suzuki–Miyaura coupling, one-carbon homologation, oxidation, allylation, and Rh-catalyzed conjugate addition are also described. Synthesis of silylboranes, including those having heteroatom functional groups at the silicon atoms, is summarized.