The book provides a comprehensive and systematic presentation of the statistical mechanics of avalanche phenomena, from self-organized criticality (SOC) and non-equilibium phase transitions to crackling noise in materials. The book consists of two parts: the first one provides a theoretical perspective, starting with the basic definition of model systems. The picture resulting from numerical simulations is interpreted in the theoretical framework of driven dissipative systems, by drawing analogies with absorbing phase transitions and depinning transitions. The second part of the book is devoted to experimental systems displaying avalanche phenomena and crackling noise, where the concept of SOC finds application as an interpretative and modelling framework. The topics covered include: fracture, plasticity, granular media, domain walls in ferromagnetic materials, vortices in superconductors, fluid in porous media, and geophysical phenomena. This book dicusses the state of the art advances in the field, and is of interest to graduate students and researchers starting in the field, and to all scientists already involved in related fields.