Unless specifically prohibited by another provision of law, an agency's authority to contract is vested in the agency head, for example, the Secretary of the Air Force or the Administrator, National Aeronautics and Space Administration. Agency heads delegate their authority to Contracting Officers, who either hold their authority by virtue of their position or must be appointed in accordance with procedures set forth in the Federal Acquisition Regulation. Only Contracting Officers may sign Government contracts on behalf of the Government. A Contracting Officer has only the authority delegated pursuant to law and agency procedures.