The aim of this book is to give a state-of-the-art presentation of suspended particulate matter (SPM) in lakes, rivers and marine areas, with a focus on the roles that SPM plays in aquatic ecosystems and on modelling. To the best of the author's knowledge, this is the first book of its kind, and this is remarkable because SPM is very important in aquatic sciences. It regulates the transport of all types of water pollutants in dissolved and particulate phases. It regulates water clarity and the depth of the photic zone, and, hence, also primary and secondary production. SPM regulates bacterioplankton production and biomass, and, thus, also mineralization, oxygen consumption and oxygen concentrations. SPM regulates sedimentation and the use of sediments as an historical archive, e.g. of water pollutants. These matters are discussed in this book, which also presents empirical and dynamical models for SPM based on the ecosystem perspective. The aim of these models is to structure existing knowledge on the factors regulating variations among and within aquatic systems of SPM in a rational and quantitative manner. This knowledge is fundamental for an understanding of the function and structure of aquatic systems. This book is intended as a textbook (mainly for Master's and Ph.D. students) in aquatic sciences, but it should also attract a considerable interest from researchers in limnology, marine ecology and environmental sciences, as well as from consultants and administrators interested in management and studies of aquatic systems. Dr. Lars Håkanson (Ph.D. in physical geography 1972, Uppsala University, Sweden) has been a professor in sedimentology (recent processes) at Uppsala University since 1992. He has been Chairman of IAEA ́s international aquatic program on Validation of Model Predictions (VAMP), 1988-1994, a member of the delegation for the Åland Foundation for the Future of the Baltic, 1989-1995 and Director of the International Association for Sediment Water Science (IASWS) 1981-1996. He was President of IASWS 1990-93. He is a member of the editorial boards of Environmental Geology and Aquatic Ecosystem Health and Management. He was awarded The Linné and Alfort Prizes for 1979. Dr. Håkanson has published 450 scientific papers and reports, including 13 international textbooks, 21 books/theses in Swedish and 20 contributions in international monographs.