And on November 2, 2000, Nasa astronaut Bill Shepherd and Roscosmos cosmonauts Yuri Gidzenko and Sergei Krikalev became the first crew to man it.
They spent four months completing tasks necessary to bring the ISS "to life", and since then, it has been continuously occupied.
More than 280 individuals have visited from 22 countries, and more recently, those numbers have included 13 very rich "space tourists".
Over the past 25 years, Nasa (United States), Roscosmos (Russia), ESA (European Space Agency), Jaxa (Japan Aerospace Exploration Agency) and CSA (Canadian Space Agency) have worked with more than a dozen countries to grow the ISS into a 109m end-to-end, living and working space that is larger than a six-bedroom house, with six sleeping quarters, two bathrooms, a gym and a 360° view bay window.
It has a football field-sized solar array, about 13km of electrical wiring, a 17m-long robotic arm (Canadarm2), and up to eight spaceships can be docked there at any one time.
The large modules and other pieces of the station were delivered on 42 assembly flights — 37 on the US space shuttles and five on Russian Proton/Soyuz rockets.
Originally, it was intended to be a laboratory, observatory and factory while providing transportation, maintenance and a low-Earth-orbit staging base for possible future missions to the Moon, Mars and asteroids.
Not all of the uses have been realised yet, but the onboard research covers a wide variety of fields including astrobiology, astronomy, physical sciences, materials science, space weather, meteorology and human research including space medicine and the life sciences.
More than 20 different research payloads can be hosted outside the station at once, including Earth sensing equipment, materials science payloads and particle physics experiments.
These days, four different cargo spacecraft deliver science, cargo and supplies — Northrop Grumman’s Cygnus, SpaceX’s Dragon, Jaxa’s HTV, and the Russian Progress.
The ISS is crewed by seven people while travelling at speeds of about 8km per second, orbiting Earth about every 90 minutes.
Russian cosmonauts Oleg Kononenko and Nikolai Chub hold the record for the longest-duration stay on the ISS, at 374 days, while Oleg Kononenko has accumulated 1111 days onboard.
The ISS is expected to have more modules added (including the Axiom Orbital Segment) and will be in service until the end of its operational life in 2030.
At that time, the plan is to "de-orbit" the space station and let it burn up in Earth’s atmosphere.
In the future, space agencies will become "customers", using areas on commercially built, owned and operated low-Earth-orbit space stations to conduct their research.
