In the present review, the development of notions about hydride transformations is described. It is shown that hydride transformations were classified as a special type of phase transition in a number of classic phase transformations. Then, the available information about reverse hydride transformations in the Pd-H system is summarized and it is shown that reverse hydride transformations in this system proceed by the mechanism of generation and growth. The C-shaped kinetic isothermal diagrams describe kinetics of direct alpha -> beta HT. Another type of kinetic diagram is typical for reverse beta -> alpha hydride transformations, and the rate of these hydride transformations just accelerates with temperature increase or hydrogen pressure decrease. Morphological peculiarities of reverse hydride transformations are described in detail. In the conclusion, a discussion of the unique role of hydrogen concentrational and hydrogen phase stresses in processes of hydride transformations is given. It has been found that these stresses are the most important thermodynamic and kinetic factors in the hydride transformation development. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.