The Battle of Buçaco (pronounced [buˈsaku]) or Bussaco was fought on 27 September 1810 during the Peninsular War in the Portuguese mountain range of Serra do Buçaco, resulting in the defeat of French forces by Lord Wellington's Anglo-Portuguese Army.

Having occupied the heights of Bussaco, a 10-mile (16 km) long ridge located at 40°20'40"N, 8°20'15"W, with a total of 26,843 British and 25,429 Portuguese, Wellington was attacked five times successively by invasion force of 65,050 French under Marshal André Masséna. Masséna was uncertain as to the disposition and strength of the opposing forces because Wellington had deployed them on the reverse slope of the ridge, where they could neither be easily seen nor easily softened up with artillery. The actual assaults were made by the corps of Marshal Michel Ney and General of Division (Major General) Jean Reynier, but after much fierce fighting they failed to dislodge the allied forces and were driven off after having lost up to 4,500 men against up to 1,356 Anglo-Portuguese casualties. However, Wellington was ultimately forced to withdraw to the Lines of Torres Vedras after his positions were outflanked by Masséna's troops.

The Third Portuguese campaign had started with the construction of the Lines of Torres Vedras and the Siege of Ciudad Rodrigo.

In 1810, Emperor Napoleon ordered Masséna to drive the British from Portugal. Accordingly, the French marshal began the siege of Ciudad Rodrigo in April. The Spanish garrison held out until 9 July when the fortress fell. The Battle of the Côa was fought soon after. The Siege of Almeida ended suddenly with a massive explosion of the fortress magazine on 26 August. With all obstacles cleared from their path, the French could march on Lisbon in strength.

It was important to delay the French until the defences being built around Lisbon, the Lines of Torres Vedras, could be completed. Using selective demolition of bridges and roads, Wellington restricted the choice of routes the French could use and slowed their advance. At the end of September, they found Wellington's army drawn up on the ridge of Bussaco. The ridge, which at its highest rising to 549 metres (1,801 ft), lies at a right angle to the main road to Coimbra and thence to Lisbon, providing one of the few and certainly the best defensive position on the French route of march.

Wellington had brought together six British infantry divisions:

In addition, the Portuguese Army (newly re-trained by the British under the direction of Lieutenant General William Carr Beresford) supplied a two-brigade Portuguese infantry division under Major General John Hamilton, and three independent Portuguese brigades led by Brigadier Generals Denis Pack, Alexander Campbell and John Coleman.

Brigadier Generals George De Grey, John Slade, George Anson and Henry Fane led four British cavalry brigades, plus four regiments of Portuguese cavalry. In batteries of six guns each, there were six British (Ross RHA, Bull RHA, Thompson, Lawson, two unknown), two King's German Legion (Rettberg, Cleeves) and five Portuguese (Rozierres, Da Cunha Preto, Da Silva, Freira, Sousa) batteries under Brigadier General Edward Howorth.