This book covers the results of investigations into the mechanisms and kinetics of thermal decompositions of solid and liquid substances on the basis of thermochemical analyses of the processes. In the framework of the proposed ideas, the main features of these reactions are explained and many problems and unusual phenomena, which have accumulated in this field are interpreted. New methods of TA measurement and calculation have been developed, which permit the precision and accuracy of determination of kinetic parameters to be increased substantially. Reliable kinetic characteristics have been obtained and the decomposition mechanisms for several tens of substances have been interpreted. These include different classes of compounds: crystalline hydrates, oxides, hydroxides, nitrides, azides, nitrates, sulfates, carbonates and oxalates.