The Pennacook, also known by the names Penacook, and Pennacock, are a North American people of the Wabanaki Confederacy that primarily inhabit the Merrimack River valley of present-day New Hampshire and Massachusetts, as well as portions of southern Maine.They are also sometimes called the Merrimack people.

An Algonquian-speaking tribe, they are more closely related to the Abenaki tribes to the west, north and east such as the Penobscot, Piguaket or Pawtucket than to the other Algonquian tribes to the south, such as the Massachusett or Wampanoag.

This similarity is both linguistic and cultural.

However, during the time of early European settlement, the Pennacook are a large confederacy that are politically distinct and at odds with their northern Abenaki neighbors.