This text emphasizes the ecological processes that influence community organization and ecosystem function in running waters. After providing an introduction to the physical and chemical circumstances of running water, there is an analysis of the biology and ecology of these systems, covering the following topics: the ecological role of autotrophic and heterotrophic energy producers; the trophic ecology of consumer organisms in lotic food webs; the community ecology of flowing waters, including herbivory, predation and competition, and their integration with abiotic factors in determining community organization; downstream drift; the dynamics of organic matter and of elements, including the concepts of mass balance and spiralling; the effects of humans on river systems; management and conservation of rivers and their biota. This book is intended to be of use to undergraduates, researchers and specialists in stream ecology and related fields.