STS-108 was a Space Shuttle mission to the International Space Station (ISS) flown by Space Shuttle Endeavour. Its primary objective was to deliver supplies to and help maintain the ISS. It was the 12th shuttle flight to visit the International Space Station and the first since the installation of the Russian airlock called Pirs on the station. Endeavour delivered the Expedition 4 crew to the orbital outpost. The Expedition 3 crew returned to Earth on Endeavour.
The International Space Station programme is tied together by a complex set of legal, political and financial agreements between the sixteen nations involved in the project, governing ownership of the various components, rights to crewing and utilization, and responsibilities for crew rotation and resupply of the International Space Station. It was conceived in 1984 by President Ronald Reagan, during the Space Station Freedom project as it was originally called.