The preparation of twenty organic B–S compounds, including members of the new classes R2NB(SR′)2, (R2N)2BSR′, (R2N)BrBSR′, and (R2N)ClBSR′, is reported. Five methods were explored, and particularly noteworthy are the general methods for synthesis of borthi-ins (XBS)n, with use of dihalogenoboranes and either HgS or (Me2SiS)3. The position of B–S compounds, relative to B–N, B–Hal, etc., in boron “conversion” and “dispalcement” series is assigned. The thioboranes have been fully characterised. Especially significant is the recognition of a triplet absorption centering upon 930 cm.–1 as diagnostic for their identification. Molar refractivities agree well with calculated values. The complexes BrB(SBun)2,2py and Br2BSBun,py have been prepared. Oxidation of a B–S compound has afforded the first boryl sulphone. Thioboranes act as 1,2-dipolarophiles with respect to isocyanates, but not isothiocyanates, carbon dioxide, or carbon disulphide. The novel thiourethanoboranes have been characterised.