There are several reasons why combining laser beams makes sense: (1) some lasers, such as fiber lasers, have good beam quality but limited output power, (2) it allows for graceful degradation, (3) it makes the overall system more modular, and (4) it distributes the cooling load. This book summarizes and describes all the known methods for combining laser beams from low-power lasers into one high-power beam on target. People often assume that, since I've written many books, I'm a rich man.  No one gets rich writing technical books.  If I had no other income except for book royalties, I'd have just enough money to purchase one cheap hamburger per day.  So, there must be other reasons for writing technical books.  I do it because I want to make a difference in this world today, and I want to leave something of myself in this world after I die.