Wassenaar (Dutch pronunciation: [ˈʋɑsənaːr] ^ⓘ; population: 26,949 in 2021) is a municipality and town located in the province of South Holland, on the western coast of the Netherlands.

An affluent suburb of The Hague, Wassenaar lies 10 km (6 mi) north of that city on the N44/A44 highway near the North Sea coast. It is part of the Haaglanden region and the Rotterdam–The Hague metropolitan area. The municipality covers an area of 62.40 km² (24.09 sq mi), of which 11.29 km² (4.36 sq mi) is covered by water.

Wassenaar is home to some of the Netherlands' richest residential neighborhoods as well as the country's most expensive street, the Konijnenlaan.

By tradition, the 12th-century Romanesque church in Wassenaar is the spot where the Northumbrian missionary Willibrord landed in the Netherlands; the high dunes to the west were not formed until later.

Wassenaar long remained an unremarkable small town, known only as the home of the House of Wassenaer. It only began to gain prominence in the 19th century when Louis Bonaparte ordered the construction of the Heerweg ("Army Road") between The Hague and Leiden, which forms the current Rijksstraatweg. In approximately 1840, Prince Frederik had the De Paauw (Peacock) palace built, where he lived for many years; it now serves as the city hall of Wassenaar.

In 1907 a railway was built, connecting Rotterdam, The Hague, Wassenaar and Scheveningen, the course of which now forms the Landscheidingsweg. Wassenaar became attractive as a residence for wealthy people from Rotterdam. Buildings such as the monumental Huize Ivicke were constructed.

Some remnants of the Atlantic wall are located on Wassenaar's beach, the Wassenaarseslag; nearly a thousand metres of underground walled tunnels are present, connecting five bunkers. The network now serves as a bat sanctuary and is no longer open to visits.

From September 1944 to March 1945 Wassenaar was one of the launch sites used by the German Luftwaffe for the V-2 rockets directed mainly towards London.