The variety of magnetic and electrical properties of ferrites is closely related to their chemical transformations in the process of synthesis and heat treatment. The book discusses the content and main goals of heat treatment, including the processes of chemical homogenization and the formation of a ceramic structure. Much attention is paid to the interaction of ferrites during heat treatment, as well as equilibrium diagrams describing the behavior of ferrite systems under different conditions of heat treatment. The discussion is based on the idea of ferrites as phases or compounds of variable composition, allowing a deeper understanding of the relationship between the physico-chemical and magnetic properties of ferrites formed during heat treatment. The monograph systematizes data on the kinetics of processes occurring during heat treatment, gives an idea of thermomagnetic processing and changes in the properties of ferrites in time. Specific examples show how to practically determine the optimal conditions for heat treatment of ferrites used in computing in microwave devices . Modern ideas about the physico-chemical nature of heat treatment processes are presented in an accessible form.