The article reviews current ideas regarding electromagnetic phenomena in single crystals. The treatment is based on the theory developed by the authors, which describes radiation of photons by charged particles and production of electron-positron pairs by photons for any energies of the incident particle and arbitrary orientation of the crystal. Attention is given to the significant enhancement of processes in an oriented single crystal in comparison with an amorphous material. The development of particular electron-photon showers is analyzed. The authors make a comparison of theoretical predictions and experimental data which demonstrates their satisfactory agreement. Practical applications of the phenomena considered are presented.