The Mason-Dixon Line is a historic boundary originally surveyed between 1763 and 1767 by Charles Mason and Jeremiah Dixon to resolve a border dispute between the colonies of Pennsylvania and Maryland. It runs along the southern border of Pennsylvania, the northern and eastern borders of Maryland, and the western border of Delaware. A small portion of the line also touches West Virginia along the southern border of Pennsylvania

. Geographically, the line is approximately at latitude 39°43′ N and extends from a benchmark south of Philadelphia eastward to the Delaware River and westward to what was then the boundary with western Virginia (now West Virginia). The line also includes the boundary between Delaware and Pennsylvania and the north-south boundary between Delaware and Maryland. The Maryland-Pennsylvania boundary is an east-west line near 39°43′20″ N but is not a perfect straight line, instead made up of adjoining segments

. Historically, the Mason-Dixon Line became known as the dividing line between the Northern free states and the Southern slave states before and during the American Civil War. Today, it still serves figuratively as a cultural and political boundary between the North and the South in the United States