Optical limiters and switches can be fabricated in a variety of ways. The simplest devices are those which utilize materials that respond nonlinearly with incident intensity. We analyze and model five different passive limiter/switch concepts which could yield practical devices. These concepts include the total internal reflection, photorefractive beam-fanning, two-photon absorption, self-focusing, and self-defocusing. The analysis is carried out for typical optical materials used in the visible and infrared and the eye for a wide range of incident-pulse widths. The strength and speed of the nonlinearities required for the fundamental performance of each limiting device is provided. Factors considered in the analysis include dynamic range, transmission, response time, and the damage threshold.