This document discusses Fourier transform infrared (FTIR) spectroscopy. It begins by introducing terahertz radiation and its applications in cancer detection and security imaging. It then explains how FTIR spectroscopy works, using an interferometer to generate a beam containing many frequencies that is passed through a sample, with the absorption measured. Computer processing via the Fourier transform is required to convert the raw data into the desired absorption spectrum. FTIR spectroscopy has the advantage over scanning spectroscopy of being faster. The document concludes by noting potential applications and advantages of FTIR spectroscopy.