Two main ways of applying the method of solid hydrothermal treatment have been considered: (a) hydrothermal modification of polycrystalline adsorbents and catalysts; and (b) hydrothermal synthesis of materials possessing regular porosity (zeolite-like, laminar and others). Modification processes of phase composition and mechanical properties of complex adsorbents and catalysts were discussed. The essential features of hydrothermal crystallization in multicomponent systems have been presented.