DS9 centers on the formerly Cardassian space station, Terok Nor. After the Bajorans liberated themselves from the long, brutal Cardassian Occupation, the United Federation of Planets is invited by the Bajoran Provisional Government to take joint control of the station, which (originally) orbits Bajor. The station is renamed Deep Space Nine.

The representatives from these varied civilizations must learn to co-exist, despite everpresent political tensions and the constant risk of war.