Following major 2005 reforms, Chile’s constitution establishes a four-year term for a popularly elected president, who is not eligible for immediate reelection (he or she may run again after a four-year hiatus). If no candidate obtains a majority, the top two finishers stage a runoff.

In the January 2006 runoff, Concertación candidate Michelle Bachelet, a Socialist, became Chile’s first female head of state by defeating the RN’s Sebastián Piñera, a conservative but maverick businessman who broke early and publicly with the dictatorship. In the December 2005 primary, Piñera had defeated UDI candidate Joaquín Lavín, who finished a strong second to Socialist Ricardo Lagos in a 2000 runoff.

Under the 1980 Pinochet-Guzmán constitution, the Congreso has a binomial electoral system by which each district (60 for deputies and 19 for senators) elects two officials, but a list or coalition must double its rivals’ votes to take both seats. In practice, this favored the conservative Alianza, whose total vote has always been smaller than that of the Concertación, though the difference is narrowing. The Congreso renews the 120-strong Chamber of Deputies and half the 38 Senate members every four years. Voting is obligatory for citizens registered, but registration itself is not.

In the December 2005 congressional elections, the Concertación obtained clear majorities in both houses for the first time since the dictatorship ended in 1989. In the Senate, its four parties totaled 20 seats against 17 by the two Alianza parties; there was one independent. In the Cámara de Diputados, the Concertación held a majority of 65 to 55.