Defense Primer: Under Secretary of Defense for Intelligence and Security [Updated December 30, 2020] [open pdf - 485KB]
From the Document: "The Under Secretary of Defense for Intelligence and Security (USD(I&S)) is a civilian official, appointed by the President and confirmed by the Senate, who reports directly to the Secretary of Defense. The USD(I&S) is the Principal Staff Assistant and advisor to the Secretary and Deputy Secretary of Defense on intelligence, counterintelligence (CI), security, sensitive activities, and other intelligence related matters. On behalf of the Secretary, the USD(I&S) also exercises authority, direction, and control over Department of Defense (DOD) intelligence and security agencies, field activities, policy, processes, procedures, and products. To give greater emphasis to the importance and scope of the USD(I&S)'s security responsibilities, including primary federal government responsibility for conducting background investigations (consistent with Executive Order 13869), Congress redesignated the position of Under Secretary of Defense for Intelligence (USD(I)) as the Under Secretary of Defense for Intelligence and Security (USD(I&S)) in the National Defense Authorization Act (NDAA) for Fiscal Year 2020 (Section 1621 of P.L. 116- 92)."
CRS In Focus, IF10523
Congressional Research Service: https://crsreports.congress.gov/