Oostburg (Zeelandic Flemish: "Wòstburg") is a town in the south-western Netherlands. It is the largest town in the municipality of Sluis, in the province of Zeeland. As of 1 January 2015, its population is 4731, down from 5008 in January 2005. It received city rights in 1237. Before 1 January 2003, Oostburg was also the name of a municipality. It merged with Sluis-Aardenburg to form the new municipality of Sluis. The municipality covered an area of 224.93 km², of which 1.05 km² was water. As well as the town of Oostburg, the former municipality also included the following towns, villages and townships: