In general, the Delaware Valley is a term used to refer to the valley where the Delaware River flows.

However, this article discusses the economic region centered on the cities on the tidal part of the Delaware Valley, including the metropolitan areas centered on Philadelphia, Pennsylvania. and Wilmington, Delaware. It is roughly the Philadelphia–Camden–Wilmington, Pennsylvania-New Jersey-Delaware-Maryland (PA-NJ-DE-MD) Metropolitan Statistical Area.

The Delaware Valley as discussed here is composed of several counties in Eastern Pennsylvania and Western New Jersey, one county in northern Delaware and one county in northeastern Maryland. The area has a population of over 6.1 million (as of the 2010 Census Bureau count). Philadelphia, being the region's major commercial, cultural, and industrial center, maintains a rather large sphere of influence that affects the counties that immediately surround it. The majority of the region's populace resides in Pennsylvania, New Jersey, and Delaware.

Delaware (ⁱ/ˈdɛləwɛər/ DEL-ə-wair) is a U.S. state located on the Atlantic Coast in the Mid-Atlantic region of the United States. It is bordered to the south and west by Maryland, to the northeast by New Jersey, and to the north by Pennsylvania. The state takes its name from Thomas West, 3rd Baron De La Warr, an English nobleman and Virginia's first colonial governor, after whom what is now called Cape Henlopen was originally named.

Delaware is located in the northeastern portion of the Delmarva Peninsula and is the second least extensive, the sixth least populous, but the sixth most densely populated of the 50 United States. Delaware is divided into three counties. From north to south, these three counties are New Castle, Kent, and Sussex. While the southern two counties have historically been predominantly agricultural, New Castle County has been more industrialized.

The history of the state's economic and industrial development is closely tied to the impact of the Du Pont family, founders and scions of E. I. du Pont de Nemours and Company, one of the world’s largest chemical companies.