The Delaware Valley also encompasses the surrounding states of Delaware, Maryland and New Jersey. The following counties in those states are considered part of this region.
The Delaware Valley is home to the "birthplace of America," Philadelphia, PA. Sites throughout the valley hosted battles between the British and colonia Americans during the Revolutionary War and Philadelphia itself saw the writing of the Delcaration of Independence and the Constitution of the United States of America. Philadelphia today is the center of the region with 6.2 million people living within it's boundaries. Neighboring Camden, rated the most dangerous city in America, was once an industrial center and today is revitalizing its downtown and waterfront with attractions like a concert arena and an exotic aquarium. Wilmington, DE to the south is the largest city in Delaware and is one of the most important banking cities in the United States.
Dialect in the Delaware Valley sounds much like its New York City counterpart to the north. Many r's are dropped. In Philadelphia, "water" is pronounced either "wudder" or "wooder." Words like "kawfee" and "hawt" with an exaggerated "o" sound have been borrowed by denizens of the New York City area.
The major airport in the Delaware Valley with schedruled service to most major cities, and certain international destinations is Philadelphia International Aiport (ICAO: PHL) 
The Delaware Valley is serviced by several interstates including the Pennsylvania Turnpike, Interstate 95, the Garden State Parkway and the New Jersey Turnpike.
The Delaware Valley is extensively served by both the national rail company Amtrak and the Southeast Pennsylvania Transportation Authority. SEPTA commuter rail extends to Newark, DE and Trenton, NJ. Southern New Jersey is also served by the Delaware River Port Authority's PATCO Hi-Speedline which is a hybrid subway and above-ground system.
Taxis can be hailed in the major cities in the Delaware Valley including Philadelphia and Wilmington. For those adventurous enough to drive in these two large, car-congested cities, parking is scarce and roads can be hectic. Defensive driving is one's best bet in Philadelphia and Wilmington, as drivers are known to be both vocal and ruthless.
In Philadelphia, two subway lines and a subway-surface line cover the city. The Broad Street Line runs north-south and the Market-Frankford Line runs east-west. The subway-surface line parallels the MFL and makes stops at smaller stations than the subway of the same direction.