Paris has inaugurated a modern electric tram line along a section of the city's inner ring road, the first time trams have run in the city since 1937.
Mayor Bertrand Delanoe rode the first tram on the new T3 line, built to offer Parisians environmentally-friendly public transport.
The line is set to carry 100,000 people a day along a crowded section on the Left Bank of the Seine.
The opening was boycotted by right-wing opposition parties.
They have opposed the 300m euro ($400m; £200m) development, calling it a waste of money.
But Mr Delanoe defended the tram project, the largest public transport project for Paris since the city's ring road was built in the 1970s.
"We need to respond to pollution with action, it's a necessity of public health and civilisation," he said.
"Half of the planet's population lives in towns today, so we need to make behaviour evolve."
Tram lines already run in some suburban areas outside Paris' city limits.
But the new tram is the first within the metropolitan area since Paris's extensive tram network was finally closed just before World War II.
Those trams, which began as horse-drawn carriages, ran from the mid-19th Century and predated the city's underground Metro system.
The new line runs through 17 stops in the city's 13th, 14th and 15th arrondissements, to link the Garigliano bridge on the city's western edge with the Porte d'Ivry to the south-east.
There are plans to expand the network to other areas of the city.
Journeys on the new line will be free during the tram's inaugural weekend, with fares after that costing the same as the bus line the tram has replaced.
The mayors of Beirut, London, Montreal, Barcelona, Bamako, Stockholm and Antananarivo were in Paris for the opening ceremony.