STS-126 was a Space Shuttle mission to the International Space Station (ISS) flown by Space Shuttle Endeavour. The purpose of the mission, referred to as ULF2 by the ISS program, was to deliver equipment and supplies to the station, to service the Solar Alpha Rotary Joints (SARJ), and repair the problem in the starboard SARJ that had limited its use since STS-120 STS-126 launched on 14 November 2008 at 19:55:39 pm EST from Launch Pad 39-A at NASA's Kennedy Space Centre with no delays or issues. Endeavour successfully docked with the station on 16 November. After spending 11 days, 16 hours, and 46 minutes docked to the station, during which the crew performed four spacewalks, and transferred cargo, the orbiter undocked on 28 November 2008. Due to poor weather at Kennedy Space Centre, Endeavour landed at Edward's Air Force Base on 30 November 2008 at 21:25 UTC (13:25 PST)

Originally scheduled to fly on STS-126 was Joan E. Higginbotham, who was a mission specialist on STS-116On 21 November 2007, NASA announced a change in the crew manifest due to Higginbotham's decision to leave NASA to take a job in the private sector. Stephen G. Bowen was originally assigned to STS-124 but was moved to STS-126 to allow Discovery to rotate Greg Chamitoff with Garrett Reisman.

STS-126 was scheduled to be a sixteen-day mission with four spacewalks, largely dedicated to servicing and repair of the Solar Alpha Rotary Joints (SARJ). An additional docked day was added to the flight plan to give the crew more time to complete their tasks. The starboard SARJ had shown anomalous behavior since August 2007, and its use has been minimized pending diagnosis and repair. Both the starboard and port SARJs were serviced. In addition to lubricating both bearings, the remaining 11 trundle bearings in the starboard SARJ were replaced. Trundle bearing assembly five was removed during an Expedition 16 EVA for further examination in December 2007.

STS-126 included the Leonardo Multi-Purpose Logistics Module (MPLM) on its fifth spaceflight. Leonardo held over 14,000 pounds of supplies and equipment. Among the items packed into the MPLM were two new crew quarters racks, a second galley (kitchen) for the Destiny laboratory, a second Waste and Hygiene Compartment (WHC) rack (lavatory), the advanced Resistive Exercise Device (aRED), two water reclamation racks, spare hardware, and new experiments. Also included in Leonardo was the General Laboratory Active Cryogenic ISS Experiment Refrigerator, or GLACIER, a double locker cryogenic freezer for transporting and preserving science experiments. The shuttle also carried irradiated turkey, candied yams, stuffing and dessert for a special Thanksgiving meal at the station, as well as an Official Flight Kit with mementos for those who supported the astronauts and helped them complete their mission successfully.

Also carried was a Lightweight MPESS Carrier (LMC) carrying a Flex Hose Rotary Coupler (FHRC) and returning a Nitrogen Assembly Tank from 'Quest' for refurbishment.