Estuaries are minor geographical features at the global scale, but have major importance for society and the world's economies. This book, with case studies from three continents, offers a perspective on estuaries as ecosystems that are intimately linked to society in both positive and negative ways. As focal points of trade, industry, energy production, fisheries, and tourism, estuaries provide a bounty of services to society; they are also centers of human population and vulnerable to the accompanying environmental stresses. This book covers a wide range of topics, from the definition and classification of estuaries, to chemical and physical properties, ecological processes, habitat values, fisheries, and tools for improving management and policy.