Studying the dynamics of a large number of particles interacting through long-range forces, commonly referred to as the "N-body problem," is a central aspect of many different branches of physics. In recent years, physicists have made significant advances in the development of fast N-body algorithms to deal efficiently with such complex problems. This book gives a thorough introduction to these so-called "tree methods," setting out the basic principles and giving many practical examples of their use. The authors assume no prior specialist knowledge, and they illustrate the techniques...