Maassluis ([maːˈslœy̯s]) is a town in the western Netherlands, in the province of South Holland. The municipality had a population of 32,230 in 2014 and covers 10.12 km (3.91 sq mi) of which 1.63 km (0.63 sq mi) water.

It received city rights in 1811. It was the setting for Spetters, filmed by director Paul Verhoeven in 1980.