The Adda (Latin: Abdua, or Addua; Lombard: Ada, or Adda) is a river in North Italy, a tributary of the Po. It rises in the Alps near the border with Switzerland and flows through Lake Como. The Adda joins the Po near Castelnuovo Bocca d'Adda, a few kilometers upstream of Cremona. The river's length is 313 kilometres (194 mi). The highest point of the drainage basin is the summit of La Spedla (a subpeak of Piz Bernina), at 4,020 metres (13,190 ft).

Towns along the river include Bormio, Tirano, Sondrio, Bellagio and Lecco (both on Lake Como), Brivio and Lodi.