The book provides a clear description of the processes involved in welding with high-performance lasers, serving as a foundation for the sizing and optimization of a laser beam welding process. Individual effects are separated as much as possible and examined from the fundamentals to descriptions using approximation formulas. Where this is not feasible, investigative methods are explained that illustrate the processes and thus provide a deeper understanding. This comprehensive overview offers a clear depiction of the processes involved in welding with high-performance lasers, forming the basis for the sizing and optimization of a laser beam welding process.