Mexicans will choose a new leader on July 1 amid rampant drug violence and a sluggish economy that have hurt the administration of President Felipe Calderon.
Four candidates are on the ballot, with Calderon himself prohibited by law from running for a second term. The campaign will officially start on Friday.
The field is clearly led by Enrique Pena Nieto, of the opposition Institutional Revolutionary Party or PRI, which ruled Mexico for most of the 20th century.
Josefina Vazquez Mota, of Calderon's National Action Party, or PAN, follows second, with most polls showing her trailing Pena Nieto by double digits.
Leftist Andres Manuel Lopez Obrador, who is standing for the Party of the Democratic Revolution (PRD), is close behind her in third place.
Whoever takes office in December will inherit a country wracked by violence, with the death toll from the drug war reaching more than 50,000 in five years. The new leader will also have to generate enough jobs to alleviate the grinding poverty that affects half of Mexico's population.
Following are profiles of the registered candidates.
ENRIQUE PENA NIETO
The telegenic Pena Nieto, 45, carries the hopes of the party that governed Mexico for 71 years until it was ousted by the PAN in 2000. While Pena Nieto has roots deep in the PRI political machine, he is presented as a new, younger and more handsome face of the party.
Governor of the State of Mexico from 2005 until 2011, Pena Nieto has suffered less from the taint of corruption than previous governors. He has made an effort to be more transparent and built his image on public works and cooperation with the neighboring Mexico City government to improve infrastructure.
Married to a glamorous Mexican soap opera star, Pena Nieto has an extended family that includes several former state governors and mayors in central Mexico, the most populous part of the country. The politicians from the area have long been extremely influential in the PRI.
After studying law and briefly teaching, Pena Nieto has been in politics for most of his working life. The sudden death of his first wife in 2007 stirred rumors of suicide but Pena Nieto weathered the storm and solidified his power base.
Pena Nieto's image has been carefully cultivated by the party. He has still made several gaffes in news conferences and interviews, but they have not hurt him badly.
Unlike PRI leaders in the 20th century, Pena Nieto is open about his Roman Catholic beliefs and has met with Pope Benedict. He also keeps his speeches short and snappy, unlike the long technical PRI sermons of old.
Critics say Pena Nieto has not been tested against rivals and has so far ignored challenges to engage in public debates.
JOSEFINA VAZQUEZ MOTA
The first female presidential candidate for a major Mexican party, Vazquez Mota, 51, has the hard job of defending an administration that has overseen unprecedented levels of drug-related bloodshed.
Serving as Calderon's education minister before becoming leader of the PAN in the lower house of Congress, Vazquez Mota won the party primary against contenders including ex-finance minister Ernesto Cordero, who was seen as the president's favorite.
The victory reflected her popularity among the PAN's grassroots, but the party has cut a less united figure in the campaign than it did during its two winning bids for the presidency in 2000 and 2006.
Vazquez Mota supports the PAN's free market policies and says she is a devout Roman Catholic like Calderon, but unlike many of her fellow party members she has expressed tolerant views on same sex marriage and abortion.
The PAN candidate grew up in a traditional middle class family in Mexico City, attended some top private universities and then worked for several years as a financial consultant and business columnist. She is married to her childhood sweetheart, businessman Sergio Ocampo, and has three children.
In 1999, Vazquez Mota came to national attention with a book, "God, Please Make Me A Widow," which discussed how she had rejected the traditional role of the Mexican housewife.
The following year she entered politics full-time, winning a seat in Congress for the PAN just as Vicente Fox was elected president. In 2001, she left her seat in Congress to become minister for social development in Fox's cabinet.
Vazquez Mota was one of the most visible figures in Calderon's 2006 election, helping him win office in a hard fought campaign against leftist Lopez Obrador. In Congress, she pushed for Calderon's reforms of labor laws and of the Mexican police but the bills were held up by PRI and PRD opposition.
A confident speaker with the media, Vazquez Mota is quick to play the card of a rising female politician in macho Mexico, where women only got the vote in 1953.
However, she has come under fire for conservative lines in her writing, such as one old article which commended the economic policies in Chile under dictator Augusto Pinochet.
It remains to be seen if she can attract many voters beyond the PAN base.
ANDRES MANUEL LOPEZ OBRADOR
The charismatic leftist Lopez Obrador came within a whisker of the presidency in 2006 but is struggling to build momentum for his campaign this year.
The mayor of Mexico City from 2000 to 2005, Lopez Obrador, now 58, built a loyal base in the capital by establishing a pension scheme and other social welfare programs. He also oversaw large-scale construction projects.
Often referred to as AMLO or "Peje" - a type of tough swamp fish in his native Tabasco - Lopez Obrador is famous for leading his supporters out on huge protest marches and making impassioned speeches condemning Mexico's "mafia" of rich and powerful oligarchs.
The silver-haired politician was born in the small town of Macuspana in Tabasco, where he began his career working with the government to help indigenous people. He first joined the PRI but abandoned it to help found the leftist PRD in 1988.
In 2006, Lopez Obrador fought a tight and divisive election against Calderon, who portrayed the leftist as an irresponsible populist who would bankrupt Mexico.
Lopez Obrador lost by less than 1 percent of the vote and led protest camps calling for a recount, declaring himself the legitimate president. The blockades held up traffic in the capital for weeks, provoking widespread criticism.
In the 2012 campaign, Lopez Obrador has taken a less confrontational approach, saying he is in favor of business but against monopolies. His new rhetoric, however, has so far failed to regain voters' enthusiasm.
The fourth candidate on the ballot, Gabriel Quadri, is not considered to have any hope of winning but could be an interesting spoiler if the race between the main candidates tightens. Quadri is standing for the New Alliance Party, or Panal, of Elba Esther Gordillo, head of the teachers' union and long one of the most powerful politicians in Mexico.
Quadri, who will take part in all the debates and has space for TV spots assigned, could launch attacks on one of the major candidates to try to influence the race.