The authors describe the electric, magnetic and other relaxational processes in a wide spectrum of materials: liquid crystals, molecular magnets, polymers, high-Tc superconductors and glasses. The book summarizes the phenomenological fundamentals and the experimental methods used. A detailed description of molecular and collective dynamics in the broad range of liquid crystals is presented. Magnetic systems, high-Tc superconductors, polymers and glasses are an important subject of matter. It is shown that the researchers working on relaxation processes in different fields of materials sciences are dealing with the same physical fundamentals, but are sometimes using slightly different terms. The book is addressed to scientists, engineers, graduate and undergraduate students, experimentalists and theorists in physics, chemistry, materials sciences and electronic engineering. Many internationally well known experts contribute to it.