A review is given of the current data on semiconducting diamonds, both natural and those prepared by doping in the course of crystal growth in the laboratory or by implantation of impurities in insulating crystals. The review deals with theoretical papers reporting calculations of the principal characteristics of the energy band structure of diamond, and with the results of experimental studies of the energy spectra, photoionization, charged-particle ionization, transport phenomena, and luminescence of semiconducting diamonds. Special attention is paid to the problem of the nature of electrically active acceptor and donor local centers. Actual and potential technical applications of secmiconducting diamonds are discussed briefly.