This is a tutorial paper on the SIMS. The SIMS is an acronym for the spectrometre interferentiel a modulation selective (selective modulation interference spectrometer), recently introduced by Marechal and Fortunato. The paper reviews the basic principles of operation, the properties, the implementation configurations, and the current investigations of the SIMS at Utah State University. The following properties make the SIMS a powerful spectroscopic instrument. It has an extremely large optical throughput. For example, the SIMS can be configured with a light gathering capability, throughput, thousands of times larger than that of a conventional slit spectrometer. The SIMS does not require a computer to recover the spectrum; it has moderate resolving power, and it has relatively rugged implementation configurations.