This site is a joint effort between NASA and USA International Space Station Payload Information Source

ISS Phases I, II, and III
ISS development is progressing through three designated phases:

Phase 1
The first phase, the Shuttle-Mir Program, began in 1995 and involved more than two years of continuous stays by astronauts aboard the Russian Mir Space Station and nine Shuttle-Mir docking missions. Knowledge was gained in technology, international space operations and scientific research.

Many of the research programs planned for the International Space Station benefit from longer stays in space. The U.S. science program aboard the Mir was a pathfinder for more ambitious experiments on the new Station.

Phase 2
In Phase 2, the knowledge gained from Phase 1 is applied to the on-orbit assembly of the ISS. Phase II concludes with the successful assembly of the U.S. and Russian components of the ISS necessary to begin Station research.

Phase 3
ISS Phase 3 development consists of final outfitting of the ISS, as the European, Japanese, and Canadian elements are transported and the Station becomes fully operational.