This book is a unique collection of experimental data in the field of internal friction, anelastic relaxation, and damping properties of metallic materials. It reviews virtually all anelastic relaxation phenomena ever published, and also most of the internal friction effects based on other types of dissipation of mechanical (elastic) energy. Furthermore, the reader is also supplied with explanations of the basic physical mechanisms of internal friction, a summary of typical effects for different groups of metals, and more than 2000 references to original papers.