Fort Amsterdam was the name of the Dutch fort that was constructed on the southern tip of Manhattan in 1625. The fort became the nucleus of the New Amsterdam settlement, which in turn would eventually become New York City. The fort is no longer existent, and the site is now occupied by the Alexander Hamilton U.S. Custom House, which currently houses the National Museum of the American Indian.

The fort was primarily intended to protect the New Netherland colony operations in the Hudson River against attack from the English and the French.

As early as 1620, the Dutch East India Company had contacted the English architect Inigo Jones asking him to design a fortification for the harbor. Jones responded in a letter with a plan for a star-shaped fortification made of stone and lime and surrounded by a moat and defended with cannons. Jones advised the company against constructing a timber fort out of haste.

The building of the fort commenced in 1625, under the direction of Wilhem Verhulst , the director of the New Netherland colony and his chief engineer Cryn Fredericks. By the end of the year, Frederick had surveyed the site. At the time, Manhattan was only lightly settled, as most of the Dutch West India Company operations were upriver along the Hudson in order to conduct trading operation for beaver pelts.

Despite Jones' plea in his letter, the plan for the masonry fortification was abandoned, however, out of the need for a hasty completion. This was due primarily to:

• the looming threat from England and France, which were also conducting beaver trade operations in North America. England, in particular, had laid claim to region as well.
• the growing threat of the Mohawk-Mahican War in the upper Hudson Valley,which itself was partially the result of the fur trade operations there.
• the fact that the company was not turning a good profit, and thus the cost of a masonry fort was deemed too high
• the lack of labor and natural resources to construct a proper masonry fort.