The Battle of Bicocca or La Bicocca (Italian: Battaglia della Bicocca) was fought on 27 April 1522, during the Italian War of 1521–26. A combined French and Venetian force under Odet de Foix, Vicomte de Lautrec, was decisively defeated by an Imperial–Spanish and Papal army under the overall command of Prospero Colonna. Lautrec then withdrew from Lombardy, leaving the Duchy of Milan in Imperial hands.

Having been driven from Milan by an Imperial advance in late 1521, Lautrec had regrouped, attempting to strike at Colonna's lines of communication. When the Swiss mercenaries in French service did not receive their pay, however, they demanded an immediate battle, and Lautrec was forced to attack Colonna's fortified position in the park of the Arcimboldi Villa Bicocca, north of Milan. The Swiss pikemen advanced over open fields under heavy artillery fire to assault the enemy positions, but were halted at a sunken road backed by earthworks. Having suffered massive casualties from the fire of Imperial-Spanish arquebusiers, the Swiss retreated. Meanwhile, an attempt by French cavalry to flank Colonna's position proved equally ineffective. The Swiss, unwilling to fight further, marched off to their cantons a few days later, and Lautrec retreated into Venetian territory with the remnants of his army.

The battle is noted chiefly for marking the end of the Swiss dominance among the infantry of the Italian Wars, and of the Swiss method of assaults by massed columns of pikemen without support from other troops. Along with the previous encounter in Cerignola, in which Colonna also participated, it was one of the first engagements in which firearms played a decisive role on the battlefield. It has been also proposed that the Spanish arquebusiers performed there the first instance of volley fire in European warfare. Historian John Fortescue described it as, "...if it were necessary to fix an arbitrary date for the first really effective use of small fire-arms in the battlefield, the day of Bicocca might well be selected."

At the start of the war in 1521, Holy Roman Emperor Charles V and Pope Leo X moved jointly against the Duchy of Milan, the principal French possession in Lombardy. A large Papal force under Federico II Gonzaga, Duke of Mantua, together with Spanish troops from Naples and some smaller Italian contingents, concentrated near Mantua. The German forces which Charles sent south to aid this venture passed through Venetian territory near Valeggio unmolested; the combined Papal, Spanish, and Imperial army then proceeded into French territory under the command of Prospero Colonna. For the next several months, Colonna fought an evasive war of maneuver against the French, besieging cities but refusing to give battle.

By the autumn of 1521, Lautrec, who was holding a line along the Adda river to Cremona, began to suffer massive losses from desertion, particularly among his Swiss mercenaries. Colonna took the opportunity this offered and, advancing close to the Alps, crossed the Adda at Vaprio; Lautrec, lacking infantry and assuming the year's campaign to be over, withdrew from the subsequent battle to Milan. Colonna, however, had no intention of stopping his advance; he launched a surprise attack on the city, overwhelming the Venetian troops defending one of the walls. Following some abortive street-fighting, Lautrec withdrew to Cremona with about 12,000 men.

By January 1522, the French had lost Alessandria, Pavia, and Como; and Francesco II Sforza, bringing further German reinforcements, had slipped past a Venetian force at Bergamo to join Colonna in Milan. Lautrec had meanwhile been reinforced by the arrival of 16,000 fresh Swiss pikemen and some further Venetian forces, as well as additional companies of French troops under the command of Thomas de Foix-Lescun and Pedro Navarro; he had also secured the services of the condottiere Giovanni de' Medici, who brought his Black Bands into the French service. The French proceeded to attack Novara and Pavia, hoping to draw Colonna into a decisive battle. Colonna, leaving Milan, fortified himself in the monastery of Certosa south of the city. Considering this position to be too strong to be easily assaulted, Lautrec attempted instead to threaten Colonna's lines of communication by sweeping around Milan to Monza, cutting the roads from the city into the Alps.

Lautrec was suddenly confronted, however, with the intransigence of the Swiss, who formed the largest contingent of the French army. The Swiss complained that they had not received any of the pay promised them since their arrival in Lombardy, and their captains, led by Albert von Stein, demanded that Lautrec attack the Imperial army immediately—else the mercenaries would abandon the French and return to their cantons. Lautrec reluctantly acquiesced and marched south towards Milan.

Colonna had meanwhile relocated to a formidable new position: the manor park of Bicocca, about four miles (6 km) north of Milan. The park was situated between a large expanse of marshy ground to the west and the main road into Milan to the east; along this road ran a deep wet ditch, which was crossed by a narrow stone bridge some distance south of the park. The north side of the park was bordered by a sunken road, which Colonna deepened, constructing an earthen rampart on the southern bank.