The Ettenmoors were a high barren region that lay on the western side of the Misty Mountains north of Rivendell and south of Angmar. The river Hoarwell flowed from its sources in the Ettenmoors to the southwest.
The Ettenmoors were also called the troll-fells, probably because the region was inhabited by Trolls. The Ettenmoors included the land of the Ettendales, which consisted of valleys reaching up into the foothills of the Misty Mountains.
The realm of Rhudaur lay between the Ettenmoors in the north and the Angle between the rivers Hoarwell and Loudwater in the south. It is speculated that Mount Gram, from where a host of Orcs attacked the Shire, was located in the Ettenmoors.
Since the Elder Days, Trolls concentrated especially around the Ettenmoors, and they increased during the rule of Angmar, that was founded in the north.
In S.A. 3320 when the realm of Arnor was founded by the Dúnedain, the Ettenmoors probably became part of Arnor.
When the kingdom of Arnor split into three successor kingdoms after the death of King Eärendur in T.A. 861, the Ettenmoors probably became a part of the kingdom of Rhudaur.
In T.A. 1975 after his defeat in the Battle of Fornost the Witch-king of Angmar fled with the remains of his troops to the north to reach his realm of Angmar and the shelter of Carn Dûm, but was pursued to the Ettenmoors where he was overtaken by the cavalry of Gondor and a force from Rivendell led by Glorfindel. After the fall of Angmar, the Trolls retreated to the east of the Misty Mountains but returned in the 28th century and even expanded westwards as far as the North Downs.
It is possible that Chieftain Arador was slain by trolls in this area in 2930.
Around November or December T.A. 3018, scouts from Rivendell investigated the Ettenmoors for any activities concerning Ringwraiths or other servants of Sauron, but they came with no warning news.
In October T.A. 3018 Gandalf after his battle with the Ringwraiths at Weathertop Gandalf fled riding on Shadowfax to the north in the hope of drawing off some of the Ringwraiths. He had to send Shadowfax away in the Ettenmoors, because he was not able to ride among the rocks there.