|Location||Between Beleriand and Eriador|
|Realms||Belegost, Nogrod, and later realms like Thorin's Halls|
|Inhabitants||Dwarves (Broadbeams, Firebeards, and Longbeards)|
|Description||Great western mountain range|
|Other names||Ered Luin, Ered Lindon|
|Events||War of Wrath|
|References||The Fellowship of the Ring, Quest of Erebor, The Silmarillion|
In the Beginning
During the creation of Arda, the Blue Mountains were meant to line up directly with the Grey Mountains of the southlands, forming the western wall of Arda. They lay parallel to the Red Mountains and Yellow Mountains that formed the eastern wall. The Blue Mountains were originally connected with the Red Mountains by the Iron Mountains which stretched across the entire north. The symmetry of Arda was broken during the wars between the Valar and Melkor in the ages before the Years of the Lamps.
Before and During the First Age
In the First Age, the Blue Mountains were an unbroken line separating Eriador from Beleriand. Seven rivers flowed from its western side, and the land these rivers flowed through was known as Ossiriand. Later, when the Green Elves settled there, the land was called Lindon, and the mountains sometimes referred to as the Ered Lindon.
The Second Age
The Blue Mountains were ruined during the War of Wrath, and at the middle of the range the sea broke through. The River Lhûn now flowed through the mountains to the Gulf of Lhûn. On the west side of the Blue Mountains a small section of Lindon remained, and here the retreating Elves built the Kingdom of Lindon, ruled by Ereinion Gil-galad, last High King of the Noldor. Its most important city was the Grey Havens, from where departing Elves left Middle-earth for Valinor. Also located here were the two regions of Forlindon to the North, with it's chief port being Forlond. And Harlindon to the South, which Harlond was its chief port.
The Dwarven cities of Nogrod and Belegost were also ruined when the Blue Mountains were broken. Nogrod in the South was completely destroyed and Belegost in the North was ruined. Most of the Dwarves migrated east to Khazad-dûm. However some remained to rebuild their ancestrial halls. The Dwarves lived mainly in the Southern chain on the East side of the mountains.