Maryland is a U.S. state located in the Mid Atlantic region of the Southern United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east. Maryland was the seventh state to ratify the United States Constitution, and three nicknames for it (the Old Line State, the Free State, and the Chesapeake Bay State) are occasionally used. Maryland is a major center for life sciences research and development. With more than 350 biotechnology companies located there, Maryland is the third-largest nexus in this field in the United States.