The Agogna (in Piedmontese Agògna) is a 140-kilometre (87 mi) stream which runs through the Italian regions of Piedmont and Lombardy. It is a left side tributary of the river Po.

The river's origin is in the area between Lake Orta and Lake Maggiore in the province of Verbano-Cusio-Ossola. It then flows south into the province of Novara and flows past Borgomanero and Cureggio before being joined by a branch of the Terdoppio. The river continues to flow south past Caltignaga and Novara. The river then crosses into the province of Pavia and into the Lomellina area (in the communes of Castello d'Agogna and Lomello) and receives its left tributary, the Erbognone.