Stream Ecology by Allan and Castillo is extensively revised and updated from the successful first edition to include major developments over the past decade. Although the subject matter is relatively advanced, this book has been written with the express goal of being accessible to students with only modest backgrounds in ecology and aquatic sciences. The First Edition was widely praised for its readability, and that emphasis is retained. The second edition opens with a new introductory chapter that sets the stage for what follows. The treatment of geomorphology and hydrology are greatly expanded from the first edition, and have been split into two, more substantial chapters. Basal energy resources, trophic roles and food web interactions are retained but thoroughly updated, particularly to include recent advances in microbial ecology and the synergies between producers and decomposers. The discussion of species interactions has been re-organized so that modern topics receive more emphasis, including trophic cascades, subsidies and food web structure. Chapters on organic matter dynamics and nutrient cycling have been substantially re-written to reflect the enormous growth in knowledge of stream metabolism and nutrient processes, the core of ecosystem functioning. The closing chapter on human impacts summarizes the status of river ecosystems and principal threats, and new material that describes advances in river management including the science of environmental flows, the successes and failures of river restoration, and the potential for ecosystem-based catchment management.