In the fiction of J. R. R. Tolkien, Beleriand was the region of northwestern Middle-earth during the First Age. Originally, the name belonged only to the area around the Bay of Balar, but in time the name was applied to the entire land. The element Beler/Balar is believed to refer to the Maia Ossë, who often dwelt at the shores of Balar.

Spoiler warning: Plot and/or ending details follow.
To the west and south it had a long shore with the Great Sea Belegaer, to the north were the highland regions of Hithlum, Dorthonion and the hills of Himring, to the east the Ered Luin (Blue Mountains) reached nearly to the sea. The land of Nevrast in the northwest was sometimes considered part of Beleriand.

The River Sirion, the chief river of Beleriand, running north to south, divided it into West Beleriand and East Beleriand. Crossing it east to west was a series of hills and a sudden drop in elevation known as Andram, the Long Wall. (The river sank into the ground at the Fens of Sirion, and reemerged below the Andram at the Gates of Sirion.) To the east of the Long Wall, was the River Gelion and its six tributaries draining the Ered Luin, in an area known as Ossiriand or the Land of Seven Rivers. The River Brethin and the River Nenning were the two lesser rivers of the western land of Falas.

In the year 583 of the First Age, Beleriand was mostly destroyed by the War of Wrath of the Valar against Morgoth. Only a small section of East Beleriand remained, and was known as Lindon. (There is however, some evidence that other parts of it still remained into the Second Age but were completely destroyed with the downfall of Númenor.)

In addition, fulfilling a prophecy, the graves of Túrin Turambar and Morwen survived as the island Tol Morwen. Likewise part of Dorthonion became Tol Fuin, and the Hill of Himring became the island of Himling. All of these together were known as the Western Isles.

Regions and kingdoms of Beleriand:

Arvernien
Forest of Brethil
Dimbar
Doriath
Estolad
Falas
Himlad
Nan-tathren (Land of Willows)
Talath Dirnen (Guarded Plain)
Taur-en-Faroth (Forest of the Hunters)
Taur-im-Duinath
Thargelion
Ossiriand or Lindon

Cities of Beleriand:

Belegost
Brithombar
Eglarest
Gondolin
Himring
Menegroth
Nargothrond
Nogrod
Vinyamar