Betazed is a class-M Federation member world, and home to the Betazoids. It is the fifth planet in the Beta Zeta system.
The (ceremonial) ruling family of Betazed is the Fifth House of Betazed. The planet's capital is Rixx.
Betazed was admitted into the Federation in 2273.
In 2366, Betazed held the Federation's biennial trade agreements. (TNG episode: "Ménage à Troi")
In 2374, the Dominion invaded Betazed while the Tenth fleet was on a training run. (DS9 episode: "In The Pale Moonlight")
Captain David Gold's son, Nathan, was visiting Ambassador Lwaxana Troi just as the Jem'Hadar attacked. Her assistant, Homn, was killed when the Dominion fired on the surface. (anthology: Tales of the Dominion War)
However, the inhabitants fought back, and eventually rid the world of Dominion forces, but not until after suffering heavy casualties themselves. (TNG novel: The Battle of Betazed)
As of 2377, Betazed had a population of 1.3 billion. (reference work: Star Trek: Star Charts)