The Penn–Calvert boundary dispute was a long-running legal conflict between William Penn and his heirs on one side, and Charles Calvert, 3rd Baron Baltimore and his heirs on the other side. The overlapping nature of their charters of land in Colonial America required numerous attempts at mediation, surveying, and intervention by the king and courts of England to ultimately be resolved. Subsequent questions over these charters have also been adjudicated by American arbitrators and the Supreme Court of the United States. The boundary dispute shaped the eventual borders of five U.S. states: Pennsylvania, Maryland, Delaware, New Jersey, and West Virginia.

William Penn was an English writer, religious thinker, and influential Quaker who founded the Province of Pennsylvania during the British colonial era. Penn, an advocate of democracy and religious freedom, was known for his amicable relations and successful treaties with the Lenape Native Americans who had resided in present-day Pennsylvania prior to European settlements in the state.