Maassluis (population: 32,847 in 2004) is a town in the western Netherlands, in the province of South Holland.
Maassluis was founded circa 1340, as a settlement next to a lock (in Dutch: sluis) in the sea barrier between the North Sea and Rotterdam. Originally called Maeslandsluys, it was part of Maesland.
Maassluis was historically dependent on the fishing industry. Its fishermen would fish mainly near the coast of the North Sea and the coast of Iceland. But in the 19th century the town became home to the tugboat company L. Smit & Co. and the marine salvage company W.A. van den Tak, which fused and became known as Smit-Tak, now a division of the world's largest salvage company Smit International. Also, there is still a large shipping agency called Royal Dirkzwager. These days it is mainly a commuter town for Rotterdam.