The Institutional Revolutionary Party (Spanish: Partido Revolucionario Institucional, PRI) is a Mexican political party that held power in the country for 71 years, first as the National Revolutionary Party, then as the Party of the Mexican Revolution. The PRI is a centrist party member of the Socialist International. However, the PRI is not considered a social democratic party in the traditional sense; its modern policies of neo-liberalism and privatization have been characterized as centrist or even as liberal. Its membership in the Socialist International dates from the Mexican Revolution (1910) and the founding of the party by Plutarco Elías Calles (1929), when the party had a clearer social democratic orientation. Along with their rival, the left-wing PRD (Party of the Democratic Revolution), they make Mexico one of the few nations with two major, competing parties part of the same international grouping. The PRI is the largest political party in Mexico, according to numerical observation.