The Beta Quadrant was the common designation for one-quarter of the Milky Way Galaxy. It was adjacent to the Alpha Quadrant and the Delta Quadrant. One-quarter of the galactic core was located in this quadrant.
In 2363, Captain Lisa Cusak and the crew of the USS Olympia began a seven-year exploration voyage in the Beta Quadrant. Following this mission, the Olympia crashed on a planet in the Rutharian sector en route back to Federation space. While escorting a convoy to the Vegan system in 2374, the crew of the USS Defiant made contact with Cusak in 2371 via a temporal anomaly.
In an alternate timeline, the USS Voyager used a quantum slipstream drive to cross the Delta and Beta Quadrants, before crashing on an Class L planet in the Takara sector, a few parsecs short of reaching the Alpha Quadrant. Also in this timeline, Starfleet Intelligence had salvaged a Borg temporal transmitter from the debris of a Borg cube in the Beta Quadrant.
When members of the Hierarchy captured Captain Janeway and forced The Doctor to obtain Voyager's warp core for them, he impersonated Janeway and told Commander Chakotay a cover story involving a fictitious R'Kaal Imperium which supposedly controlled "thousands of parsecs from here to the edge of the Beta Quadrant."
- Klingon Empire
- Romulan Star Empire
- United Federation of Planets