This textbook provides a comprehensive introduction to the fundamentals of laser beam generation and offers a good overview of the most common laser beam sources. Didactically, the textbook is characterized by a step-by-step derivation of the results, which not only conveys the basics but also trains their application. This didactic approach is also evident in the more detailed treatment of rate equations than usual. In the current edition, modes in optical fibers and the derivation of the black body spectrum have been included, and illustrations are presented in color for faster information transfer.