This article reviews the theoretical and experimental studies on a number of the thermodynamic aspects of superionic conduction, the intensive study of which began in the past decade. We discuss the relation of superionic conductivity to the disordering of one of the sublattices of the crystal, disordering phase transitions caused by the interaction of point defects, and the mechanism of polymorphic transitions associated with partial disordering. We analyze the effect of jumpwise variation of the ionic conductivity induced by an external electric field, the thermodynamics of domain states in superionic conductors, and the effect of pressure on the phase transitions and the ionic conductivity.