Zohran Mamdani is reveling in what he calls a "new era" for New York City.
He was officially sworn in just after midnight Thursday, but politicians and other supporters gathered at City Hall in the afternoon for a larger ceremony.
Mamdani is the city's first Muslim mayor, its first of South Asian descent and the first to be born in Africa.
At 34, he is also the city's youngest mayor since the late 19th century.
The democratic socialist takes office after a historic campaign made "affordability" a national buzzword across the political spectrum.
U.S. Sen. Bernie Sanders administered the public oath of office to Mamdani today.