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 Trezzo sull'Adda Bridge, constructed in 1377, had a single arch of , the longest bridge arch built before the introduction of metal in bridge construction.
The lower course of the Adda historically marked the border between the Republic of Venice and the Duchy of Milan, as established by the Treaty of Lodi in 1454. Several significant battles have been fought along its banks, including the Battle of Lodi in 1796, where Napoleon defeated Austrian forces.