Saarlouis is a city in Saarland, Germany, capital of the district of Saarlouis. In 2017, the town had a population of 34,758. Saarlouis, as the name implies, is located on the River Saar. It was built as a fortress in 1680 and named after Louis XIV of France.

Even today, the fortress dominates the city's hexagonal floor plan. Beside the buildings made by Vauban, there are also some constructions left from the 19th century when the Prussians got control over the town. After 1887, some parts of the fortress were slighted, but many buildings and places, e.g. the casemates, some barracks and the Great Market with the Commander's Office and the Vauban island, a former ravelin with a memorial for Michel Ney can still be seen today.

Saarlouis was famous for its nearby steel and iron ore production and its nearby mining facilities. Today, the Ford Motor Company's Saarlouis Body & Assembly is the city's largest employer, producing the Ford Focus and Ford Kuga. The plant in the Roederberg suburb is one of Ford's most efficient facilities worldwide.

The industrial port in Saarlouis-Roden is Germany's 8th largest inland port. Saarlouis is also a manufacturer of chocolate.