A review of the current status of theoretical and experimental investigations of the magnetism of actinides and their compounds is given. The electron structure of actinides is considered and information is given on the magnetism of actinide metals. The problem of the actinide valence in compounds (specifically, the phenomenon of mixed valence) is analyzed. A review is given of the models which allow for the collectivization of the 5f electrons and for their hybridization with other groups of electrons in actinide compounds. Variation of the magnetic properties with the degree of collectivization is studied. Descriptions are given of the characteristics of the critical behavior and of magnetic excitations in actinide compounds. Data are provided on the magnetic anisotropy and on magnetoelastic interaction in actinide compounds.