The book summarizes the work and the results of a five year government funded research project as well as subsequent research results about high power diode laser systems and their application in the field of materials processing. The entire technology chain, starting from the semiconductor technology, over cooling mounting and assembly, beam shaping and system technology down to the applications in processing of several kinds of materials (metals, polymers) are treated in the book. Theoretical models, a wide field of important parameters and practical hints and tips are provided. The book is the most extensive work on high power diode laser systems and materials processing applications.