Whileit is hoped that in this review most of the fundamental developments in infrared spectroscopy which appeared in the literature during the two-year period prior to November 1961 are discussed, it is immediately admitted that much interesting material has not been included. This is partly a reflection of the reviewer's interests, but it is also probable that much was inadvertently overlooked. Useful new data, usually in the form of spectra used in confirming molecular structures, appear in many papers devoted to organic chemistry, but the spectroscopic data are frequently not mentioned