US Department of Defense

The Office of the Secretary of Defense (OSD) is the main civilian staff element supporting the U.S. Secretary of Defense within the Department of Defense (DoD). It plays a crucial role in policy development, planning, resource management, fiscal oversight, and program evaluation. OSD functions similarly to the Executive Office of the President, assisting the Secretary in managing the entire Department.

OSD includes the offices of the Secretary and Deputy Secretary of Defense, along with several Under Secretaries overseeing areas such as research, acquisition, policy, and personnel. The office is staffed by presidential appointees confirmed by the Senate, including assistant secretaries and general counsel. The OSD provides strategic direction and administrative oversight to ensure the U.S. military is prepared and effective in fulfilling its mission, which encompasses warfighting, humanitarian aid, peacekeeping, and homeland security.