The third Star Trek television series takes place on a space station instead of a starship. The station was originally built by the Cardassians, but now belongs to the Bajorans, who've asked the Federation for assistance in rebuilding their world. The station is situated in a strategic region of space, just outside the Bajoran wormhole, which leads to the mysterious Delta quadrant.

Deep Space Nine is commanded by Benjamin Sisko, a Federation Officer who was discovered to be the Bajoran Emissary in the very first episode. The Emissary is a religious figurehead, able to communicate with the Bajoran Prophets, non-corporeal beings who exist in the wormhole.

The station holds a melting pot of beings: human, Bajoran, Ferengi, Cardassian, Trill and Klingon. It is also home to the Alpha Quadrant's only shape-shifter, Odo. Odo's people come from the Delta Quadrant and become one of the Federations greatest enemies.