Joko Widodo, the charismatic outsider who won Indonesia's presidency, made a call for national reconciliation and unity as he was sworn in.
Popularly known as Jokowi, the 53-year-old took the oath of office at a ceremony held at parliament in Jakarta.
The former Jakarta governor is the first president not to have come from the military or political elite.
Elected in July, the former furniture exporter and son of a carpenter now leads the world's third-largest democracy, with a population of about 250 million people.
US Secretary of State John Kerry and Australia's Prime Minister Tony Abbott were among those who attended the inauguration.
"We used to have our transfers of power marked by bloodshed," said an elderly Indonesian man to me today. "Today - we have this: a huge party."
Indonesia is celebrating the inauguration of its new president in style, with dancers decked out in traditional costumes, a marching band and thousands of people lining up to catch a glimpse of Jokowi on the main thoroughfare.
One man told me he had taken the day off work and brought his young daughters to witness this event because they should know what kind of man makes a "good president". Another woman, a school teacher, said that Jokowi was someone "like her" and that's why she is so thrilled he's become the leader of her country.
It was smiles all around, and a real feeling of festivity in the air. Although Mr Widodo has tough challenges to face in the future, today it was about celebrating the moment and leaving the hard work till tomorrow.