Saint-Quentin-en-Yvelines is a new town and an agglomeration community in the French department of Yvelines. It is one of the original five villes nouvelles of Paris and was named after the Saint Quentin Pond, which was chosen to become the town's centre. The town was built from a greenfield site starting in the 1960s. Its area is 119.2 km2. In 2018, Saint-Quentin-en-Yvelines had a population of 228,312. It is part of the much larger Paris metropolitan area, and is around 25 km (16 mi) west of the centre of Paris.

Yvelines is a department in the western part of the Île-de-France region in Northern France. In 2019, it had a population of 1,448,207. Its prefecture is Versailles, home to the Palace of Versailles, the principal residence of the King of France from 1682 until 1789, a UNESCO World Heritage Site since 1979. Yvelines' subprefectures are Saint-Germain-en-Laye, Mantes-la-Jolie and Rambouillet.