STS-91 is the ninth flight of the Shuttle-Mir Phase 1 docking missions. The crew brought back Andrew Thomas, the last long-duration American crew member flown on the Russian Space Station Mir. The mission marked the end of the Shuttle-Mir Phase 1 Program and opened the way for Phase Two: construction of the International Space Station. The crew patch depicts the rendezvous of the Space Shuttle Discovery with the Space Station Mir. The flags of the United States and Russia are displayed at the top of the patch and both countries are visible on the Earth behind the two spacecraft. The names of the American crew members surround the insignia on the outer areas, with the name of Cosmonaut Valery Ryumin in Cyrillic at the lower right.

The Alpha Magnetic Spectrometer (AMS) is an international payload planned to fly in the payload bay of Discovery. Two thin golden streams flowing into the AMS represent charged elementary particles. The detection of antimatter in space will help scientists better understand the physics and origins of the universe.