Institutional Revolutionary party, Span. Partido Revolucionario Institucional (PRI), Mexican political party. Established in 1929 as the National Revolutionary party by former President Plutarco Calles, it brought together the country's governmental, military, and agricultural leaders in a program of socioeconomic reform. In 1938 it was renamed the Mexican Revolutionary party, and in 1946 it acquired its present name. During the rest of the century all Mexican presidents and most officials belonged to the PRI, which was often accused of corruption and electoral fraud, the most clear-cut national example of the latter being the 1988 presidential election. Its victory margins decreased in the 1980s and 90s, and it lost some state elections to its opponents, but the party still remained Mexico's dominant political group.

In 1994 the PRI's presidential candidate, Luis Donaldo Colosio Murrieta, was assassinated; the party's new candidate, Ernesto Zedillo Ponce de León, won the presidency by a narrow margin. In the 1997 National Congress elections the party lost its majority in the lower house, although it remained the largest party. Zedillo worked to modernize and democratize both Mexico and the party.

In 1999 the PRI broke with the tradition of having presidents pick their own successors and held its first presidential primary. Nonetheless, in the 2000 national elections, the PRI candidate, Francisco Labastida Ochoa, lost to Vicente Fox Quesada, of the National Action party (PAN), ending more than 70 years of PRI control of the national government. The 2006 elections saw Roberto Madrazo, the PRI candidate for president, place third, and the party also came in third in terms of the vote for members of Mexico's congress.

The PRI nonetheless continued to be the nation's largest party in terms of local and state government officeholders, and when Mexico experienced an economic downturn in 2009 the party won a plurality in the lower house of Congress. The PRI regained the presidency in 2012, when its candidate, Enrique Peña Nieto, the former governor of Mexico state, won, and with its allies won a lower house majority in 2012 and 2015.

See J. Castañeda, The Inheritance (1999).