Expedition 27 was the 27th long-duration expedition to the International Space Station (ISS), starting on 16 March 2011. Expedition 27 saw numerous notable events, including the undocking of the Progress M-09M and Kounotori 2 spacecraft, the arrival of the Soyuz TMA-21 and Progress M-10M spacecraft, and the final rendezvous with the ISS of NASA's Space Shuttle Endeavour, on its last mission, STS-134. The expedition ended on 23 May 2011 with the departure of the Soyuz TMA-20 spacecraft, although command of the station was ceremonially handed over to the crew of Expedition 28 on 22 May.

The International Space Station (ISS) is a large space station assembled and maintained in low Earth orbit by a collaboration of five space agencies and their contractors: NASA, Roscosmos (Russia), JAXA (Japan), ESA (Europe), and CSA (Canada). The ISS is the largest space station ever built. Its primary purpose is to perform microgravity and space environment experiments.