Methyl isothiocyanate has been studied in the infra-red region from 10,000 to 250 cm-1 as vapour, solid, and melt, while the Raman spectrum has been recorded in the molten condition. The molecule is close to a symmetric top and the bands of the vapour exhibit contours generally similar to that type of molecule. A satisfactory assignment of all fundamentals has been made. Of interest is the pseudo-symmetric NCS stretching mode which has been assigned to the parallel band at 676 cm-1 in the vapour. In the Raman spectrum, the corresponding mode is observed as a strong polarized line at 656 cm-1.