The Po Valley, Po Plain, Plain of the Po, or Padan Plain is a major geographical feature of Northern Italy. It extends approximately 650 km in an east-west direction, with an area of 46,000 km² including its Venetic extension not actually related to the Po river basin; it runs from the Western Alps to the Adriatic Sea. The flatlands of Veneto and Friuli are often considered apart since they do not drain into the Po, but they effectively combine into an unbroken plain, making it the largest in Southern Europe.
The plain is the surface of an in-filled system of ancient canyons extending from the Apennines in the south to the Alps in the north, including the northern Adriatic. In addition to the Po and its affluents, the contemporary surface may be considered to include the Savio, Lamone and Reno to the south, and the Adige, Brenta, Piave and Tagliamento of the Venetian Plain to the north, among the many streams that empty into the north Adriatic from the west and north.
Geo-political definitions of the valley depend on the defining authority.