A name for the range of peaks in the northwest of Middle-earth that ran from north to south and marked the western edge of Eriador. They were also known as the Blue Mountains, and in Elvish as either Ered Luin or Ered Lindon. Beyond them to the west, during the First Age, lay the wide lands of Beleriand, but after the War of Wrath at the end of that Age, only the narrow land of Lindon remained. The mountains themselves were reduced by that catalysm, and the Sea broke through the central part of the range to form the Gulf of Lhûn.

The name 'Western Mountains' was used by the Men who dwelt on their eastern side, for whom they presented a barrier to the mysterious lands beyond. The War of Wrath was little more than a rumour to these Men, remembered only in legends. When the Númenóreans returned to Middle-earth after six centuries, the Men of Middle-earth were astounded to discover that the Edain beyond the Western Mountains had not only survived the War, but founded a powerful kingdom across the Great Sea.