Space Shuttle Atlantis (Orbiter Vehicle designation: OV‑104) is a retired Space Shuttle orbiter vehicle which belongs to NASA, the spaceflight and space exploration agency of the United States. Atlantis was manufactured by the Rockwell International company in Southern California and was delivered to the Kennedy Space Center in Eastern Florida in April 1985. Atlantis is the fourth operational and the second-to-last Space Shuttle built. Its maiden flight was STS-51-J made from October 3 to 7, 1985.

Atlantis embarked on its 33rd and final mission, also the final mission of a space shuttle, STS-135, on July 8, 2011. STS-134 by Endeavour was expected to be the final flight before STS-135 was authorized in October 2010. STS-135 took advantage of the processing for the STS-335 Launch on Need mission that would have been necessary if STS-134's crew became stranded in orbit. Atlantis landed for the final time at the Kennedy Space Center on July 21, 2011.

By the end of its final mission, Atlantis had orbited the Earth a total of 4,848 times, traveling nearly 126,000,000 mi (203,000,000 km), which is more than 525 times the distance from the Earth to the Moon.

Atlantis is named after RV Atlantis, a two-masted sailing ship that operated as the primary research vessel for the Woods Hole Oceanographic Institution from 1930 to 1966.

The space shuttle is now on display at the Kennedy Space Center Visitor Complex.

Space Shuttle Atlantis lifted off on its maiden voyage STS-51-J on October 3, 1985. This was the second shuttle mission that was a dedicated Department of Defense mission. It flew one other mission, STS-61-B (the second shuttle night launch) before the Challenger disaster temporarily grounded the shuttle fleet in 1986. Among the five Space Shuttles flown into space, Atlantis conducted a subsequent mission in the shortest time after the previous mission (turnaround time) when it launched in November 1985 on STS-61-B, only 50 days after its previous mission, STS-51-J in October 1985. Atlantis was then used for ten flights from 1988 to 1992. Two of these, both flown in 1989, deployed the planetary probes Magellan to Venus (on STS-30) and Galileo to Jupiter (on STS-34). With STS-30 Atlantis became the first Space Shuttle to launch an interplanetary probe.

During the launch of STS-27 in 1988, a piece of insulation shed from the right solid rocket booster struck the underside of the vehicle, severely damaging over 700 tiles and removing one tile altogether. The crew were instructed to use the remote manipulator system to survey the condition of the underside of the right wing, ultimately finding substantial tile damage. Due to the classified nature of the mission, the only images transferred to the mission control center were encrypted and of extremely poor quality. Mission control personnel deemed the damage to be "lights and shadows" and instructed the crew to proceed with the mission as usual, infuriating many of the crew. Upon landing, Atlantis became the single-most-damaged shuttle to successfully land. The survival of the crew is attributed to a steel L band antenna plate which was positioned directly under the missing tile. A similar situation would eventually lead to the loss of the shuttle Columbia in 2003, albeit on the more critical reinforced carbon-carbon.

During STS-37 in 1991, Atlantis deployed the Compton Gamma Ray Observatory. Beginning in 1995 with STS-71, Atlantis made seven straight flights to the former Russian space station Mir as part of the Shuttle–Mir program. STS-71 marked a number of firsts in human spaceflight: 100th U.S. crewed space flight; first U.S. Shuttle-Russian Space Station Mir docking and joint on-orbit operations; and first on-orbit change-out of shuttle crew. When linked, Atlantis and Mir together formed the largest spacecraft in orbit at the time.