The Battle of Betazed was a surprise Dominion offensive against the Federation member world of Betazed during the Dominion War in 2374.

The Jem'Hadar had secretly assembled a large invasion force in the Kalandra sector, which Starfleet had believed was too far from Dominion territory to represent a major threat. At the same time, the Tenth Fleet was caught out of position at the start of the invasion during a training exercise. The disadvantage was compounded by the relative weakness of Betazed's antiquated defenses.

Ultimately, the Dominion conquered the planet and its outlying colonies in only ten hours – a humiliating defeat for the Federation. (DS9: "In the Pale Moonlight")

Several weeks later, the Dominion attempted to form a supply line running from Betazed to the Argolis Cluster, hoping to eventually launch an attack on Vulcan. (DS9: "The Reckoning")

Later that year, the Second Fleet launched at least three attacks against the Dominion positions on the planet, but the continual Dominion reinforcements and the fortification of the planet stopped them from succeeding. (DS9: "The Sound of Her Voice")