This report summarizes the results of an investigation of several different types of optically activated light switches based on third-order nonlinear optical effects. Two optical switches utilizing the change of refractive index induced in a nonlinear medium by an intense light beam are described: one utilizes a single-pass and the other a multiple-pass (interferometric) geometry. Results of a search to find new media with large nonlinearities are given, and the possibility of increasing the nonlinearity of commonly used media by Raman-type resonant enhancement is discussed. The theoretical and experimental behavior of Fabry-Perot interferometer switch with a nonlinearly absorbing intracavity medium is also presented. In some cases, the switch could be activated by anomalously low pump powers, and possible mechanisms for this effect are discussed. The results of a literature search on the photorefractive effect are presented along with the results of an experimental effort to measure the photorefractive effect in Ge:SiO2. (Author)