The Battle of São Mamede (Portuguese: Batalha de São Mamede, pronounced: [ˈsɐ̃w̃ mɐˈmɛð(ɨ)]) took place on June 24, 1128 near Guimarães and is considered the seminal event for the foundation of the Kingdom of Portugal. Portuguese forces led by Afonso Henriques defeated forces led by his mother Teresa of León and her lover Fernão Peres de Trava. Following São Mamede, the future king styled himself "Prince of Portugal". He would be called "King of Portugal" in 1139 and was recognised as such by neighbouring kingdoms in 1143.

In late 11th century, Henry of Portugal, a knight from Burgundy and descendant of king Robert II, was in search of adventure in Hispania. He fought the Moors along with Alfonso VI of León. In honour of his fights in Hispania, the King gave him the County of Portugal. This gift came with a reinstated title; because of attempts by the previous holder some years earlier to assert independence, it had been suppressed. Henry became count of Portugal and Theresa, one of Alfonso's daughters, his wife.

São Mamede can refer to: