The U.S. Marine Corps is a very unique military organization that has been at the forefront of American defense and national security for more than 235 years. While modeled off of the Royal Marines, the U.S. Marine Corps has become distinctive in terms of its size, the strength of its institutional culture because of its historical achievements, its relationships to the other U.S. military services, and its continuing central role in American force structure and power projection capabilities. This entry discusses the history of the U.S. Marine Corps, the corps’ distinctive culture, and differences—sometimes rivalry—between the Marine Corps and the other services.