The Under Secretary of Defense for Research and Engineering (USD(R&E)) serves as the primary advisor to Department of Defense (DOD) leadership on all matters pertaining to the Department's Research and Engineering (R&E) enterprise, technology development and transition, developmental prototyping, experimentation, and administration of testing ranges and activities. USD(R&E) has the lead responsibility within the Department for synchronizing Science & Technology (S&T) efforts across the DOD, the Joint Staff and the Services.

The USD(R&E) also serves as the Chief Technology Officer (CTO) of the Department and is tasked with the imperative mission of ensuring continuous advancement of technology and innovation within the DOD enterprise. As the CTO, the USD(R&E) advises the Secretary of Defense on all matters related to research; engineering; manufacturing; developmental test and evaluation; and technology development, innovation, and protection activities and programs in the DOD and occurring internationally. The USD(R&E) also establishes priorities across those matters to ensure conformance with Office of the Secretary of Defense's policy and guidance.

The USD(R&E) also has the oversight lead for critical capabilities managed by defense agencies and field activities including the Defense Advanced Research Projects Agency (DARPA), Missile Defense Agency (MDA), and Space Development Agency (SDA) as well as the Defense Science and Innovation Board offices.