Publisher Summary This chapter discusses the fourier transform infrared (FTIR) spectroscopy of retinoids, and presents the FTIR spectra of 15 retinoids along with band positions which correlate with the retinoid structures. FTIR spectroscopy offers sufficient instrumental sensitivity, accuracy, and speed of analysis to be the method of choice. The wavelength multiplexing advantage and high energy throughput allow FTIR to be used in conjunction with low signal applications as might be the case where small quantities of material are to be analyzed or where the analysis method itself lacks efficient spectral throughput (e.g., diffuse reflectance). There are several versatile new methods for analysis which may prove to be of immense value on retinoid mixtures. In particular, attenuated reflectance cylinders allow measurement of flowing aqueous streams, such as the effluent of high-performance liquid chromatography (HPLC) systems. The ordinate performance of better quality FTIR spectrometers permits adequate blanking of the solvent concentration. Diffuse reflectance permits examination of HPLC effluent by allowing the carrier solvent to evaporate, leaving the analyte physisorbed on KCI powder. Photoacoustic spectroscopy allows examination of powders, films, or liquids without the need for sample preparation or correction for Kristiansen dispersion. All of these promise potent new alternatives for accurate and quantitative study of small quantities of retinoids. The chapter also discusses summary of absorption bands, and the purification procedures and infrared analysis.