The Dominion War is an extended plot concept developed in a number of story arcs of Star Trek: Deep Space Nine, an American science-fiction television series produced by Paramount Pictures. In the fictional Star Trek universe, the Dominion War is a conflict between the forces of the Dominion, Cardassian Union and, later, the Breen Confederacy against the Alpha Quadrant alliance of the United Federation of Planets, Klingon Empire and, later, the Romulan Star Empire.

The primary setting of much of the series is aboard the fictional Starfleet controlled space station Deep Space Nine, located above the planet Bajor. In the series this space station was moved so it was situated near a wormhole which provided instantaneous travel to the Gamma Quadrant, a region on the other side of the galaxy. During season two of Deep Space Nine, the Dominion is introduced. Over the course of season two and three more information is introduced, until the conflict escalated in season four, particularly in the episodes Homefront and Paradise Lost. The Dominion War arcs present themes that challenge the values of the characters in a manner not attempted in earlier series of Star Trek, and have received a mixed critical response. Developing the plot of the Dominion War also altered the manner in which the series was scripted, shifting the emphasis from an episodic to a serialized narrative format.