The 2010 US Census indicates that 39% of the US population, or 123.3 million people, live in Coastal Shoreline Counties which comprise less than 10% of the US land area. This results in a population density that is 4.2-times the national average. Similar dense population occurs in coastal areas worldwide. Barrier islands constitute a major coastal environment. Barrier islands are separated by tidal inlets which serve as essential navigation channels connecting harbors within the estuaries and the open ocean. Barrier island beach and tidal inlet are parts of an inter-connected system and should be understood and managed as such. This book discusses beach–inlet interaction in terms of sediment exchange among various morphologic features and processes that drive the sediment exchange. Balancing valuable sediment resources in a beach–inlet system is essential to modern shore protection and coastal management.