A commercially available Michelson interferometer has been adapted to meet the needs of our research. Transmission and reflection measurements of solid state materials can be made over the wavelength range of 25-1000 micro (400-10 cm(-1)). Provision has been made for the samples in each case to be studied from 4 degrees K to 700 degrees K with suitable cryostats and heated sample holders. These devices can easily be interchanged in the interferometer and also in a single beam far ir vacuum gratings pectrometer so that the measurements can be duplicated when necessary, using conventional spectroscopic techniques. The interferometer has the unique advantage of covering a broad frequency range without changing the operating conditions. A suitable choice of beam splitter thickness and ionic crystal powder filter combinations provides maximum efficiency in the area of interest. The region beyond 250 micro shows a rapid deterioration in signal to noise, and the relative merits of various cooled detectors and the Golay detector have been studied. Polarization measurements on solids have also been of interest, and various polarizers have been investigated. Applications of interferometry applied to a number of solid state problems are described. These include the dielectric dispersion in perovskites, compound semiconductors, internal molecular and lattice vibrations in inorganic materials and other related compounds. The relative advantages of single-sided vs double-sided interferograms in terms of accurate intensity measurements are compared. Examples of each are discussed.