Fragmentation and coagulation are two natural phenomena that can be observed in many sciences and at a great variety of scales—from, for example, DNA fragmentation to formation of planets by accretion. This book, by the author of the acclaimed LГ©vy Processes, is the first comprehensive theoretical account of mathematical models for situations where either phenomenon occurs randomly and repeatedly as time passes. This self-contained treatment develops the models in a way that makes recent developments in the field accessible. Each chapter ends with a comments section in which important aspects not discussed in the main part of the text (often because the discussion would have been too technical and/or lengthy) are addressed and precise references are given. Written for readers with a solid background in probability, its careful exposition allows graduate students, as well as working mathematicians, to approach the material with confidence.