This book offers a comprehensive review of how plastic pollution is affecting fresh and marine waters, and what the current challenges in plastic waste assessment and management in the aquatic environment are. Plastic waste comprises particles with heterogeneous physicochemical properties such as large size-range, different shapes and polymer types with various additives determining their environmental fate and risk. This complexity raises several open research questions which are explored in this book. Examples are the plastic uptake by aquatic organisms, degradation processes as well as sources and sinks in the environment. Readers will discover real case studies of plastic pollution detection and management in different parts of the world, including Asia, America and Europe, which provide an integrated overview of the global scope of this issue. This book and the companion volume Plastics in the Aquatic Environment - Part II: Stakeholders' Role Against Pollution are valuable resources to students, researchers, policymakers and environmental managers interested in plastic pollution and working towards its reduction.