This document discusses Fourier transform infrared spectroscopy (FTIR). It begins by defining a spectrometer and describing how FTIR obtains infrared spectra using an interferometer and Fourier transform. It then explains the basic components and working of an FTIR, including advantages like higher sensitivity, accuracy and resolution compared to dispersion spectrometers. Specific advantages like Fellgett's multiplex advantage and improved signal-to-noise are covered. Finally, common applications of FTIR are listed.