STS-134 (ISS assembly flight ULF6) was the penultimate mission of NASA's Space Shuttle program and the 25th and last spaceflight of Space Shuttle Endeavour. This flight delivered the Alpha Magnetic Spectrometer and an ExPRESS Logistics Carrier to the International Space Station. Mark Kelly served as the mission commander. STS-134 was expected to be the final space shuttle mission if STS-135 did not receive funding from Congress. However, in February 2011, NASA stated that STS-135 would fly "regardless" of the funding situation. STS-135, flown by Atlantis, took advantage of the processing for STS-335, the Launch on Need mission that would have been necessary if the STS-134 crew became stranded in orbit.

Changes in the design of the main payload, AMS-02, as well as delays to STS-133, led to delays in the mission. The first launch attempt on 29 April 2011 was scrubbed at 12:20 pm by launch managers due to problems with two heaters on one of the orbiter's auxiliary power units (APU). Endeavour launched successfully at 08:56:28 EDT (12:56:28 UTC) on 16 May 2011, and landed for the final time on 1 June 2011.