The United States Marine Corps (USMC) is a branch of the United States military responsible for providing force projection from the sea, using the mobility of the U.S. Navy to rapidly deliver combined-arms task forces and is one of seven uniformed services. While administratively under the Department of the Navy, the U.S. Marine Corps is a separate branch of the military, often working closely with US Naval forces for training, transportation, and logistic purposes.

Originally organized as the Continental Marines on November 10 1775 as naval infantry, the Marine Corps has evolved in its mission with changing military doctrine and American foreign policy. The Marine Corps has served in every American armed conflict including the Revolutionary War. It attained prominence in the 20th century when its theories and practice of amphibious warfare proved prescient and ultimately formed the cornerstone of the Pacific campaign of World War II. By the mid 20th century, the Marine Corps had become the dominant theorist of amphibious warfare. Its ability to respond rapidly to regional crises has made it, and continues to make it, an important body in the implementation and execution of American foreign policy.

The United States Marine Corps, with 186,342 active duty and 40,000 reserve Marines as of November 30, 2007, is the second smallest of the United States' armed forces (the United States Coast Guard is the smallest, about one fifth the size of the Marine Corps.) The Corps is nonetheless larger than the entire armed forces of many significant military powers; for example, it is larger than the active duty Israel Defense Forces.