The ISS started as a joint project and there are 5 organizations taking part in it: NASA (United States), Roscosmos (Russia), JAXA (Japan), ESA (Europe), and CSA (Canada). The first component of the ISS was launched in 1998 and only 2 years later, on 2 November 2000, the first long-term residents arrived at the station in low Earth orbit. The first expedition launched on October 31, 2000 and landed on March 21, 2001 with a crew of three: an American astronaut, William M. Shepherd, and two Russian cosmonauts, Sergei Krikalev and Yuri Gidzenko. Expeditions refer to permanent ISS crews and exclude resupply missions and space tourists.

The current crew aboard the ISS is Expedition 60 commanded by Aleksey Ovchinin, who transferred from Expedition 59 together with American flight engineers, Nick Hague and Christina Koch. The remaining 3 members of the crew, Aleksandr Skvortsov, Luca Parmitano and Andrew Morgan, are scheduled to join them on the 20th of July, 2019. The expedition will last until October 2019 when Soyuz-MS-12 will undock from the station.

The ISS is a microgravity and space environment research laboratory where the crews conduct various experiments in a number of fields (biology, human biology, physics, astronomy, meteorology, and others). The station is also used to test various flight components and systems required for missions to the Moon and Mars. One of the experiments conducted by the crew involved sending frozen mice embryos to the ISS to test the effects of radiation from the sun and cosmic sources. The embryos will then be sent back to Earth to be implanted into surrogate mothers where scientists would observe their lives and possible changes in their lifespan, cancer development, and gene mutations.

The current record holder and the person who spent the most time in space (879 days) is RKA cosmonaut Gennady Padalka who was aboard Mir, a space station that was operated by the Soviet Union and later by Russia and was deorbited in 2001 and the ISS. The people who spent the longest time aboard the International Space Station are Mikhail Kornienko and Scott Kelly who went on a year-long mission in March 2015 and spent 340.4 days in total aboard the spacecraft. Kelly was also part of the Astronaut Twin Study, where one twin brother spent a year in space while the other spent the same amount of time on Earth. NASA compared the data and found several long-lasting changes, including those related to alterations in DNA and cognition.