Mexico long had a closed, state-dominated economy, but since entering the General Agreement on Trade and Tariffs in 1986, it has signed more free trade agreements than almost any other country, and privatized almost every corner of the economy except oil and electricity.

Now, though, Lopez Obrador talks a talk not heard in Mexico since the 1960s: He wants to build more state-owned oil refineries and encourages Mexicans to "not to buy abroad, but to produce in Mexico what we consume."

Combined with a deep sense of nationalism and his own place in history, Lopez Obrador's inauguration is likely to be the most home-grown, populist handover of power in decades.

After taking the official oath of office at the Chamber of Deputies, Lopez Obrador plans to hold another ceremony later in the day on Mexico City's main square, where a leader of Mexico's indigenous communities will bestow a traditional symbol of authority — a ceremonial wooden staff known as a "baston." A grand celebration featuring traditional music will be held in the square.

The country's 65-year-old new leader is moving the presidential office fully back to the centuries-old National Palace that lines one side of the square, while refusing to live at the luxurious, heavily guard presidential residence six miles (nine kilometers) to the west. He will reside instead at his private home.

Lopez Obrador gained prominence as a leftist politician leading protests against oil pollution in his swampy native state of Tabasco, though he hasn't given any indication that he will cancel private oil exploration contracts or pull out of Mexico's free trade agreements with 44 countries.

Still, it is clear that the first big change in direction from three decades of "neoliberal" policies of free markets and small government will occur in his six-year term.

"We've had enough neoliberalism. Do we have to applaud it?" Lopez Obrador said in September. "Why don't they accept that neoliberal policies were a failure, that they only benefited a small minority, impoverished the majority of people, and caused violence?"

Lopez Obrador won a crushing victory in the July 1 elections after two previous, unsuccessful runs for the presidency and he is the country's first president since the Mexican Revolution to rise to prominence as a protest leader. He sees his inauguration as a historic "fourth transformation" of Mexico, following independence from Spain, the liberal reforms that broke the church's dominance in the 1850s and the 1910-1917 revolution.

His predecessor, Enrique Pena Nieto, leaves office with a historically low approval rating, which in several polls ranged from 20 percent to 24 percent. Pena Nieto failed to rein in Mexico's rising homicide rate or deal with thousands of Central American migrants camped out on the border, leaving both intractable issues as the biggest immediate challenges facing Lopez Obrador.