Fourier transform infrared (FTIR) spectroscopy provides a powerful tool for probing the terrestrial atmosphere. Solar absorption FTIR spectroscopy can be used to measure atmospheric abundances of tropospheric and stratospheric trace gases, while emission spectroscopy also provides information about clouds and the radiation budget.  In this talk, I will describe FTIR measurements being made at the University of Toronto Atmospheric Observatory and the Polar Environment Atmospheric Research Laboratory (PEARL) in the high Arctic, and will introduce the Canadian FTIR Observing Network (CAFTON).  Several applications of these measurements will be discussed, including identification of the sources of air pollution over Toronto, detection of smoke plumes from biomass burning events in the Arctic, and quantification of Arctic stratospheric ozone depletion.