La Chaux-de-Fonds is a Swiss city of the district of La Chaux-de-Fonds in the canton of Neuchâtel. It is located in the Jura mountains at an altitude of 1000 m, a few kilometres south of the French border. After Geneva and Lausanne, it is the third largest city of Romandie, the French-speaking part of the country, with a population of (as of December 2011^[update]) of 37,843..

The city was founded in 1656. Its growth and prosperity is mainly bound up with the watch making industry. It is the most important centre of the watch making industry in the area known as the Watch Valley. Completely destroyed by a fire in 1794 La Chaux-de-Fonds was rebuilt following a grid street plan, which was and is still original among Swiss cities. Karl Marx said about the very special urban design of the city that it was a "city-factory". The famous architect Le Corbusier, the writer Blaise Cendrars and the car maker Louis Chevrolet were born there. La Chaux-de-Fonds is a renowned centre of Art nouveau.

In 2009, La Chaux-de-Fonds and Le Locle, its sister city, have jointly been awarded UNESCO World Heritage status for their exceptional universal value.