The top two candidates are Sheinbaum, a physicist and former mayor of Mexico City, and Gálvez, a former senator and outspoken tech entrepreneur who has often adhered to progressive politics.
Several factors favor Sheinbaum and her Morena party; above all, perhaps, is López Obrador's high approval rating. Sheinbaum has pledged to continue López Obrador's agenda, in large part by consolidating some of his major infrastructure projects, carrying out his austerity measures and preserving his social welfare programs.
Millions of Mexicans have benefited from direct cash transfers and fuel and electricity subsidies under López Obrador's administration. But he has also sought to undermine watchdog and electoral institutions and given the military an outsize role in politics and the economy.
By contrast, Gálvez has pledged a coalition government with a plurality of voices that defends democratic checks and balances. She also proposes to demilitarize the country gradually, withdraw the armed forces from civilian duties and redirect them to fight organized crime, reflecting her argument that the government hasn't done enough to quell the high levels of cartel violence afflicting Mexico.
However, many voters see the parties that represent Gálvez as responsible for the legacy of corruption that Mexico has struggled to shake off.
Voters see rising cartel violence as a top election issue. With a few exceptions, the current government has struggled to control the killings, disappearances and acts of extortion ravaging the country.
The violence has not spared this year's election. Dozens of mayoral hopefuls and local officials have been killed, and more are targeted every month in what analysts say is an even bloodier election season than that of 2018.
Corruption is another major issue for voters. For years, corruption levels in Mexico have stayed flat, despite the current administration's promise to end the problem. Public institutions continue to operate without transparency. Federal and state governments have reduced the autonomy of key anticorruption agencies and constrained their budgets and staffs.
There is also a migration crisis. Even as Mexico has increased enforcement and detained more migrants than it has in at least two decades, high numbers of people continue to pass through its southern border to try to reach the United States.
So far, Sheinbaum has dominated the presidential race, with a lead between 24 and 27 percentage points over Gálvez.
Although a few opinion polls give an advantage to the governing Morena party in Congress, which already holds a majority, it is unclear whether it will win two-thirds of the seats. Without this supermajority, a Morena party under Sheinbaum would have to negotiate with the opposition to pass laws.
On election night, preliminary results will be provided in real time by the National Electoral Institute. The vote counts that determine the final result will take place from June 5 to June 8.