Constructed wetlands with horizontal sub-surface flow (HF CWs) have been used for wastewater treatment for more than four decades. HF CWs are used around the world for many types of wastewater, including municipal sewage, agricultural and industrial wastewaters, runoff waters, wastewaters containing endocrine-disrupting chemicals, and landfill leachate. This book fills a gap in the literature by providing an extensive, worldwide overview of this treatment technology. Special attention is paid to assessing the use of this treatment technology in individual countries and treatment performance of various HF CWs with respect to major pollutants in different types of wastewater. The book provides a broad base of knowledge, including: processes occurring in wetland soils and overlying water various types of constructed wetlands for wastewater treatment detailed information about design parameters, functioning, operation and maintenance, and costs of HF CWs evaluations of treatment efficiency of HF CWs under diverse conditions information on the global use of HF CWs for various types of wastewater The inclusion of case studies from over 50 countries and more than 250 colour photos that illustrate the science makes this an invaluable text. This book will be useful not only to wetland scientists, teachers, and engineers, but also to landscape planners, ecologists, wastewater-treatment designers and governmental decision-makers.