Oostzaan.

Oostzaan is a municipality and a town in the Zaanstreek, Netherlands, in the province of North Holland. The municipality had a population of in. Oostzaan has a total area of of which 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.

In the 17th century Oostzaan had its own pirate, named Claes Compaen. Originally sailing from the Netherlands as a legal pirate captain, in the possession of pirate letters, he soon began to raid ships for his private account, from the English Channel, to the Mediterranean Sea and the African-Atlantic coast into even the Caribbean Sea. He liquidated the booty on the coast of Ireland, later in Salé and the Barbary Coast. A street in Oostzaan is named for Claes Compaen.

The town has a Reformed church with a cruciform groundplan, the Great Church (1760), which contains two ship models that recall the days when Oostzaan was an important sea-faring community. In the Oostzijderveld area of Oostzaan stands a windmill, De Windjager (The Wind Hunter).