Katoomba is the main town and council seat of the City of Blue Mountains in New South Wales, Australia, and is the administrative centre of Blue Mountains City Council.

Situated on the Great Western Highway and the Great Western Railway, Katoomba is home to the Three Sisters, 102 km (63 mi) by road west of Sydney Central Business District and 39 km (24 mi) south-east of Lithgow. Katoomba railway station serves the town. Katoomba is located on the lands of the Dharug and Gundungurra Aboriginal peoples.

Katoomba is a base for bush and nature walks in the surrounding Blue Mountains. At the 2021 census, Katoomba had a population of 8,268 people.

Kedumba or Katta-toon-bah is an Aboriginal term for "shining falling water" or "water tumbling over hill" and takes its name from a waterfall that drops into the Jamison Valley below the Harrys Amphitheatre escarpment. Previously, the site was known as William's Chimney and Collett's Swamp. In 1874 the locality was named The Crushers after the name of the railway station that served a nearby quarry. The name Katoomba was adopted in 1877 and the town achieved municipality status in 1889.

For thousands of years, the Blue Mountains were home to Aboriginal peoples, specifically, the Gundungurra and Darug tribes. They knew the area as kedumba, meaning shiny, falling waters. Many of them were forced to move from their ancestral lands to Aboriginal settlements such as "The Gully", a tract of land in south Katoomba, as part of discriminatory policies established at the beginning of the 20th century. It was used as a summer encampment by the Darug and Gundungurra peoples long before the arrival of white settlers. Settlements on the Blue Mountains before 1950 led to the relocation of many Aboriginal families to "The Gully".

Between 1955 and 1957, dozens of the inhabitants of "The Gully" were forcibly evicted in order to clear the land for a racetrack being developed by a group of local businessmen. By 1958, at least 27 children from the area had also been taken from their families.

Today, there are still many traditional Aboriginal peoples living in the Blue Mountains, where there are now a number of cultural sites that walk visitors through the region's rich past and share the customs and heritage of the local tribes.

Katoomba and nearby Medlow Bath were first developed as tourist destinations towards the end of the 19th century when a series of hotels were built and then repeatedly extended.^{[citation needed]}