The Philadelphia, Wilmington and Baltimore Railroad (PW&B) was an American railroad that operated independently from 1836 to 1881. Headquartered in Philadelphia, it was greatly enlarged in 1838 by the merger of four state-chartered railroads in three Mid-Atlantic states to create a single line between Philadelphia and Baltimore.
In 1881, the PW&B was purchased by the Pennsylvania Railroad (PRR), which was at the time the nation's largest railroad. In 1902, the PRR merged it into its Philadelphia, Baltimore and Washington Railroad.
The right-of-way laid down by the PW&B line is still in use today as part of Amtrak's Northeast Corridor and the Maryland Department of Transportation's MARC commuter passenger system from Baltimore to Maryland's northeast corner. Freight is hauled on the route; formerly by the Conrail system and currently by Norfolk Southern.