The United States Army Corps of Engineers (USACE) is an engineer formation of the United States Army that has three primary mission areas: Engineer Regiment, military construction, and civil works. The day-to-day activities of the three mission areas are administered by a lieutenant general known as the commanding general/chief of engineers. The chief of engineers commands the Engineer Regiment, comprising combat engineer, rescue, construction, dive, and other specialty units, and answers directly to the Chief of Staff of the Army. Combat engineers, sometimes called sappers, form an integral part of the Army's combined arms team and are found in all Army service components: Regular Army, National Guard, and Army Reserve. Their duties are to breach obstacles; construct fighting positions, fixed/floating bridges, and obstacles and defensive positions; place and detonate explosives; conduct route clearance operations; emplace and detect landmines; and fight as provisional infantry when required. For the military construction mission, the commanding general is directed and supervised by the Assistant Secretary of the Army for installations, environment, and energy, whom the President appoints and the Senate confirms. Military construction relates to construction on military bases and worldwide installations.

For the civil works mission the commanding general is directed and supervised by the Assistant Secretary of the Army, also appointed by the President and confirmed by the Senate. Army civil works consists of three congressionally authorized business lines: navigation, flood and storm damage protection, and aquatic ecosystem restoration. Civil works is also tasked with administering the Clean Water Act Section 404 program, recreation, hydropower, and water supply at USACE flood control reservoirs, and environmental infrastructure. The civil works staff oversee construction, operation, and maintenance of dams, canals and flood protection in the U.S., as well as a wide range of public works throughout the world. USACE has 37,000 civilian and military personnel, making it one of the world's largest public engineering, design, and construction management agencies. Some of its dams, reservoirs, and flood control projects also serve as public outdoor recreation facilities. Its hydroelectric projects provide 24% of U.S. hydropower capacity. It is headquartered in Washington, D.C. and has a budget of $7.8 billion (FY2021).The corps's mission is to "deliver vital public and military engineering services; partnering in peace and war to strengthen our nation's security, energize the economy and reduce risks from disasters."Its most visible civil works missions include:

Planning, designing, building, and operating locks and dams. Other civil engineering projects include flood control, beach nourishment, and dredging for waterway navigation.

Design and construction of flood protection systems through various federal mandates.

Design and construction management of military facilities for the Army, Air Force, Army Reserve, and Air Force Reserve as well as other Department of Defense and federal government agencies.

Environmental regulation and ecosystem restoration.