This book is derived from a Seminar at the Waterways Experiment Station, Coastal Engineering Research Center, Vicksburg, Mississippi held on November 7-8, 1989. It presents a state-of-the-art review of the design, analysis, and hydraulic model testing of concrete armor units used in coastal rubble mound structures. In addition, prototypes of concrete armor units are presented and analyzed as are current design procedures. Finally, research needs are identified.