The most important results of theoretical studies of crystallization of a three-dimensional electron gas are presented. The crystallization criterion, magnetic field effects, viscous-liquid model, and possibility of experimental realization of Wigner ordering are considered. The results of experimental studies in compensated semiconductors published during the last two decades are analyzed in detail using the concepts of Wigner crystallization. It is shown that there is not a single convincing experimental proof of the existence of Wigner crystallization, and that all known experimental results can be explained in a noncontradictory way by the magnetic-field-induced localization of electrons in potential wells created by randomly distributed impurities.