The theoretical literature on plasmons in inversion layers is briefly reviewed. Predictions of the plasmon dispersion can be tested in experiments in which far infrared radiation is coupled to inversion layer plasmons by a grating structure forming the gate of an MOS device. A description of the far infrared transmission of such a device aids in interpreting the experimental results. The results to date generally show a remarkable agreement with simple theory, although interesting deviations are seen at low densities. Some recent work at plasmon wave numbers up to q ⋍ 0.14 kF is presented. © 1980, All rights reserved.