INSTITUTIONAL REVOLUTIONARY PARTY
Partido Revolucionario Institucional (PRI)

For 70 years, the Institutional Revolutionary Party, or PRI, has ruled Mexican politics. Though some consider the party's reign an autocracy, the PRI is the world's longest-governing political party.

The PRI began as a coalition of labor and agrarian groups consisting primarily of the working class and poor. The party -- described as "left wing" -- is still credited for much of the social reform experienced in Mexico following the country's civil revolution.

But, despite decades of rule, cracks in the party's solidarity are starting to show. In 1988, a group of prominent PRI members broke away to form an opposition party called the Partido Revolucionario Democrático (PRD), or the Democratic Revolutionary Party. In 1997, its founder, Cuauhtémoc Cárdenas was elected mayor of Mexico City, placing opposition authority in the country's second most-powerful post. The PRI also lost its majority in the lower house of Congress as opponents accused the party of corruption.

The party will offer its first primary presidential contest in 1999. In previous years, the nominee was chosen by the incumbent president under a system called "tapadismo" or "el dedazo."