The centre-left politician Alan Garcia has been sworn in as president of Peru for a five-year period.
Mr Garcia says he will not repeat the mistakes of the past
Leaders from Latin America and other parts of the world have been attending inauguration ceremonies, which mark his return to office after 16 years.
Mr Garcia has vowed to make the fight against poverty his top priority.
Peruvians will be hoping he does not repeat the errors of his first term - 7,000% inflation, a bloody conflict with rebels and corruption allegations.
In his inauguration speech, Mr Garcia vowed to fight poverty, restore Peru to an investment-grade debt rating and cut government expenses.
"Peru's economy and its exports have grown, but on the other hand, we face a social catastrophe. Either the poor win this time or we all lose and face social upheaval," said Mr Garcia.
Mr Garcia also outined a plan to spend $1.6bn (£860m) on building roads, schools and health clinics in rural areas where poverty is most severe.
BBC South America correspondent Daniel Schweimler says many in Peru now see Mr Garcia as a president by default.
In the first round of voting in April he came from behind to sneak into second place and a run-off vote against the inexperienced nationalist former army officer, Ollanta Humala.
Many then voted for Alan Garcia simply because they were frightened of Mr Humala and his radical proposals - others hoped that Mr Garcia would have learnt from experience, our correspondent says.
Mr Garcia says he has. And, Peru is in a better condition than it was when, aged 36, he became the country's youngest president in 1985. The rebel insurgency is over and the economy is in a healthier state.
But despite the strong economic growth the country has enjoyed under the outgoing President Alejandro Toledo, poverty levels remain high, with more than half of all Peruvians living below the poverty line.
And, says our correspondent, the opposition backing the defeated Ollanta Humala is strong and many view Mr Garcia's mandate with a mixture of cynicism and resignation.