Dr. Alexandros I. Stefanakis is an Environmental Engineer, with Diploma and Doctoral degrees from the Department of Environmental Engineering, Democritus University of Thrace, Greece. He also holds a MSc degree in the field of Hydraulic Engineering from the Department of Civil Engineering of the same university. His M.Sc. Thesis and Ph.D. Dissertation were focused on ecological treatment of wastewater and sludge using natural systems, focusing on constructed wetlands (CWs). He has published 11 papers in international peer-reviewed scientific journals, several papers in conference proceedings, technical reports, lecture notes and book chapters. He has conducted experiments in various CW systems and has participated in many scientific research programs, mainly as a team member and senior researcher. He has taught at the undergraduate level regarding environmental protection, delivers seminars in postgraduate studies programs and has been involved in international conference organizing. He has also supervised and trained various undergraduate students during their diploma thesis implementation. Dr. Christos Akratos received his diploma and doctoral degrees from the Department of Environmental Engineering, Democritus University of Thrace, Greece, and now is a Lecturer at the Department of Environmental and Natural Resources Management, University of Western Greece. Dr. Akratos has a great experience in constructed wetlands starting from his doctoral dissertation, and the majority of his publications deal with wastewater treatment with constructed wetlands. He has published 21 refereed journal papers, and has participated as a research team member in 14 research programs, most of them in the area of wastewater treatment in constructed wetlands. Dr. Vassilios A. Tsihrintzis is a Professor of Ecological Engineering and Technology and Director of the Laboratory of Ecological Engineering and Technology of the Department of Environmental Engineering, Democritus University of Thrace, Xanthi, Greece. He is a civil engineer and has M.Sc. and Ph.D. degrees in Environmental Engineering from the University of Illinois at Urbana-Champaign. Dr. Tsihrintzis' research interests concentrate, among others, in the fields of natural systems for wastewater treatment with emphasis on constructed wetlands and water resources engineering and management. His published research work includes more than 100 papers in peer-reviewed scientific journals and over 250 papers in conferences. He has also authored or co-authored books/book chapters on operations research, urban hydrology and runoff quality management, and constructed wetlands for wastewater and runoff treatment, among others. He has participated as a PI or team member in various research projects in the USA, the EU and Greece. Dr. Tsihrintzis has supervised more than 60 graduate and post-graduate student theses and 12 doctoral dissertations. He regularly teaches, among others, the course Natural Wastewater Treatment Systems, which is directly related to the proposed book. He has also served as the Head of the Department of Environmental Engineering for several years.