The major components of the Earth's atmosphere, nitrogen, oxygen and argon, are essentially transparent to infrared radiation. Most of the minor and trace gases in the atmosphere have significant infrared absorptions, which provide a means of measuring their abundance. For many years, we have been using the infrared as a remote sensing tool. As Fourier Transform systems (FTS) have developed, they have been increasingly used in our work. We primarily use two techniques for atmospheric measurements: solar absorption spectra and atmospheric emission spectra. In the solar absorption case, the sun is used as an intense source, and the measurement is similar (in principle) to that carried out routinely in the laboratory. Unfortunately, no reference (vacuum) path is readily available, the sample (atmosphere) is not under uniform temperature or pressure conditions and the composition is not uniform. Despite the complications, accurate determinations of gas amounts can be made in many cases, and path lengths unattainable in the laboratory can yield significant information about the molecular spectroscopy of some compounds. Interferometer systems have advantages for recording solar spectra in the infrared: relatively small size for comparable resolution and a highly accurate frequency scale. In most cases there is no multiplex advantage, but the throughput may be higher. FTS can also cover broad spectral intervals, which allows quantification of several gases simultaneously. The atmosphere is a very weak infrared source, and instrument sensitivity is of primary importance. FTS may or may not have a multiplex advantage, but it still provides an accurate frequency scale and substantial throughput.