The Atlas-Agena was an American expendable launch system derived from the SM-65 Atlas missile. It was a member of the Atlas family of rockets, and was launched 109 times between 1960 and 1978. It was used to launch the first five Mariner uncrewed probes to the planets Venus and Mars, and the Ranger and Lunar Orbiter uncrewed probes to the Moon. The upper stage was also used as an uncrewed orbital target vehicle for the Gemini crewed spacecraft to practice rendezvous and docking. However, the launch vehicle family was originally developed for the Air Force and most of its launches were classified DoD payloads.

The Atlas-Agena was a two-and-a-half-stage rocket, with a stage-and-a-half Atlas missile as the first stage, and an RM-81 Agena second stage. Initially, Atlas D missiles, redesignated as the LV-3, were used as the first stage. These were later replaced by the standardized Atlas SLV-3, and its derivatives, the SLV-3A and B. The final Atlas-Agena launch used an Atlas E/F.