Matías Barrio y Mier (1844–1909) was a Spanish law academic and a Carlist politician. He served as a scholar of jurisprudence at various universities, though mostly in Oviedo (1881-1892) and Madrid (1892-1909), and authored manuals used by students until the 1930s. He is best known, however, as the Carlist political leader (1899-1909). As a Traditionalist he served 9 terms in the Cortes, initially during the rule of Amadeo I (1871-1872) and then during the Restoration period (1891-1903, 1905-1909).