OSIRIS-REx was a NASA asteroid-study and sample-return mission that visited and collected samples from 101955 Bennu, a carbonaceous near-Earth asteroid. The material, returned in September 2023, is expected to enable scientists to learn more about the formation and evolution of the Solar System, its initial stages of planet formation, and the source of organic compounds that led to the formation of life on Earth. Following the completion of the primary OSIRIS-REx (Regolith Explorer) mission, the spacecraft is planned to conduct a flyby of asteroid 99942 Apophis, renamed as OSIRIS-APEX (Apophis Explorer).

OSIRIS-REx was launched on September 8, 2016, flew past Earth on 22 September 2017 and rendezvoused with Bennu on 3 December 2018. It spent the next two years analyzing the surface to find a suitable site from which to extract a sample. On 20 October 2020, OSIRIS-REx touched down on Bennu and successfully collected a sample. OSIRIS-REx left Bennu on 10 May 2021 and returned its sample to Earth on 24 September 2023, subsequently starting its extended mission to study 99942 Apophis, where it will arrive in April 2029.

Bennu was chosen as the target of study because it is a "time capsule" from the birth of the Solar System. Bennu has a very dark surface and is classified as a B-type asteroid, a sub-type of the carbonaceous C-type asteroids. Such asteroids are considered primitive, having undergone little geological change from their time of formation. In particular, Bennu was selected because of the availability of pristine carbonaceous material, a key element in organic molecules necessary for life as well as representative of matter from before the formation of Earth. Organic molecules, such as amino acids, have previously been found in meteorite and comet samples, indicating that some ingredients necessary for life can be naturally synthesized in outer space.

The cost of the OSIRIS-REx mission is approximately US$800 million, not including the Atlas V launch vehicle, which is about US$183.5 million. The OSIRIS-APEX extended mission costs an additional US$200 million. It is the third planetary science mission selected in the New Frontiers program, after Juno and New Horizons. The principal investigator is Dante Lauretta from the University of Arizona, having taken over in 2011 after the original PI Michael Julian Drake died four months after the mission won approval from NASA.

OSIRIS-REx was the first United States spacecraft to return samples from an asteroid. Previous asteroid returns include the Japanese probes Hayabusa, which visited 25143 Itokawa in 2010, and Hayabusa2, which visited 162173 Ryugu in June 2018.

Overall management, engineering, and navigation for the OSIRIS missions are provided by NASA's Goddard Space Flight Center, while the University of Arizona's Lunar and Planetary Laboratory provides principal science operations. Lockheed Martin Space Systems built the spacecraft and provides mission operations. The science team includes members from the United States, Canada, France, Germany, the United Kingdom, and Italy.

After traveling for approximately two years, the spacecraft rendezvoused with asteroid 101955 Bennu in December 2018, and began 505 days of surface mapping at a distance of approximately 5 km (3.1 mi). Results of that mapping were used by the mission team to select the site from which to take a sample of at least 60 g (2.1 oz) of material of the asteroid's surface. Then a close approach (without landing) was carried out to allow extension of a robotic arm to gather the sample.

Following the successful collection of material (121.6 grams (4.29 oz)), the sample was returned to Earth in a 46 kg (101 lb) capsule similar to that which returned the samples of Comet 81P/Wild on the space probe Stardust. The return trip to Earth was shorter than the outbound trip. The capsule landed by parachute at the Utah Test and Training Range on 24 September 2023 and was transported to the Johnson Space Center for processing in a dedicated research facility.