The i.r. spectra of benzothiazole and those of 29 of its derivatives, mono, di, and trisubstituted have been analyzed. In each series, at least one compound has been studied in the vapor state, except the heterocycles having a substituent in position 7. Three Raman spectra, one of which is the benzothiazole, have also been examined. The ν(CH) stretching and γ(CH) out-of-plane deformation vibrations have been assigned, as well as the majority of the other fundamentals of benzothiazole.Four dichloro and one trichloro derivatives have been synthetized, in order to make easy the interpretation of the γ(CH) vibrations.