Nonequilibrium processes resulting from the interaction of high-temperature superconductors with electromagnetic radiation are considered from microwave to optical range. Emphasis is laid on the dependence of surface or dc resistance on external parameters ͑temperature, bias current, modulation frequency, magnetic field, radiation power, and frequency͒, which is characteristic of every nonbolometric response mechanism considered by us. The most frequently used methods for monitoring the response of HTSC to electromagnetic radiation are described.