The ISS has been continuously inhabited since 2000. The first long-duration crew, Expedition 1, arrived aboard Soyuz TM-31 on 2 November 2000 and began living aboard the station.
Expedition 1 consisted of NASA astronaut William Shepherd and Russian cosmonauts Yuri Gidzenko and Sergei Krikalev. They launched from Baikonur Cosmodrome on 31 October and docked two days later. Their mission lasted 136 days, ending in March 2001.
The date can be confusing because the ISS began assembly earlier. The Zarya control module launched in 1998, and astronauts visited the partly assembled station before permanent occupation began. Thus, 1998 marks the start of construction and temporary human visits, while 2000 marks the beginning of an uninterrupted human presence.
Expeditions have continued through crew exchanges, with astronauts and cosmonauts typically spending several months aboard. The station became a permanently staffed laboratory rather than merely an assembly project.