Nestor Kirchner, Argentina's first elected president since the country's economy collapsed 18 months ago, has been sworn into office.
Helping hand for President Kirchner, left, from his predecessor Eduardo Duhalde
Supporters crowded along a wide boulevard outside the ornate Capitol building in Buenos Aires for a ticker-tape parade after the brief ceremony.
The inauguration was seen as a new beginning for a country struggling to steady itself after five years of recession, a $141bn debt default and deep currency devaluation.
A centre-left politician from Argentina's long-dominant Peronist Party, President Kirchner has promised to defend domestic jobs and industry after more than a decade of unbridled free market policies.
A day of lavish ceremony began when caretaker President Eduardo Duhalde had a traditional hot chocolate with his staff, then attended Mass.
Since winning the presidency, Mr Kirchner has attacked US-backed free market reforms and promised a multi-billion-dollar public works programme to stimulate the economy.
"We are not fulfilling our debt commitments," he said.
"But we cannot pay at the cost of delaying eduction and the good health of Argentina's children.
"I have come to offer you a dream, to build truth and justice, and to again have an Argentina that includes everyone and is for
everyone," he went on.
Turning to a long-standing grievance, he pledged to support Argentina's claim to the British territory of the Falkland Islands, or Malvinas, over which the two countries fought a war in 1982.
"We come from the southern part of the fatherland, from the land of the culture of the Malvinas and the continental glaciers, and we will unyieldingly maintain our claim for sovereignty over the Malvinas Islands," he said, to applause from the audience.
Analysts say President Kirchner economic plan remains vague for reviving South America's third-largest economy.
His challenges include shrinking a bloated public sector, restructuring the economy an establishing a new relationship with International Monetary Fund (IMF).
The jobless rate remains at a near record 18% with more than half the population living in poverty.
Mr Kirchner was denied the opportunity to win a clear popular mandate when his rival Carlos Menem withdrew before the second round of the election, and there were questions about just how much support he could claim.
But opinion polls give him 70% approval ratings and the BBC's Peter Greste in Buenos Aires says there is a clear sense of hope that perhaps Mr Kirchner is the leader the long-suffering Argentines have been looking for.
But to turn this country around he will need either extraordinary political skills, or extraordinary luck, our correspondent says - the new president faces enormous problems and has very little time.