The Blue Mountains is a mountainous region in New South Wales, Australia. It borders on Sydney's metropolitan area, its foothills starting approximately 50 kilometres west of the state capital.

The Blue Mountains is a mountainous region in New South Wales, Australia. It borders on Sydney's metropolitan area, its foothills starting approximately 50 kilometres west of the state capital. The area begins on the west side of the Nepean River and extends westward as far as Coxs River.

Consisting mainly of a sandstone plateau, the area is dissected by gorges up to 760 metres deep. The highest point of the range is 1,190 metres above sea level. A large part of the Blue Mountains is incorporated into the Greater Blue Mountains Area World Heritage Site, consisting of seven national park areas and a conservation reserve.

The Blue Mountains area includes the local government areas of the City of Blue Mountains, the City of Hawkesbury, the City of Lithgow and Oberon.