America's Marine Highway system accommodates the water-borne movement of passengers and non-bulk freight between origins and destinations otherwise served solely by roads and railways. Its corridors run parallel to many of the nation's most important land-based routes and connectors. These corridors are important components of the nation's broader domestic marine transportation system, which consists of 25,320 miles of navigable waterways, including rivers, bays, and channels, and many thousands of additional miles on the Great Lakes Saint Lawrence Seaway System and deep sea routes. For much of the early history of the United States, the network of waterways was the primary means of interstate commerce and transportation for goods and people. As a result, the majority of America's large metropolitan areas, as well as the preponderance of the U.S. population, are located along the coasts and navigable waterways. This book provides an overview of the current elements and benefits of water transportation, with a focus on a more environmentally sustainable transportation system; the marine highway and national defence; and impediments of new and expanded marine highway services.