Oostzaan (Dutch pronunciation: [oːstˈsaːn]) is a municipality and a town in the Zaanstreek, Netherlands, in the province of North Holland. The municipality had a population of 9,757 in 2019. Oostzaan has a total area of 16.08 km2 (6.21 sq mi) of which 4.55 km2 (1.76 sq mi) is water. Oostzaan—together with Westzaan and Assendelft—are considered the "mother towns" of the Zaanstreek (the region around the River Zaan), of which they are the three oldest towns. Oostzaan also played a role in the VOC and WIC shipping and shipbuilding.