Theresa of Portugal (Portuguese: Teresa or Tereza, [t(ɨ)ˈɾezɐ]; Archaic Portuguese: Tarasia; 1151 – 1218) was Countess of Flanders by marriage to Philip I, Count of Flanders, and Duchess of Burgundy by marriage to Odo III, Duke of Burgundy. She was the daughter of the Portuguese king Afonso I and Matilda of Savoy. She served as co-regent of Portugal with her brother during the illness of their father Afonso I of Portugal from 1172 until 1173, and regent of Flanders during the interim period after the death of her spouse and the accession of his heir.