London's Dockland's Light Railway (DLR) is now being operated by French transport group Keolis.
The group, a joint venture led by the SNCF subsidiary and the Spanish-owned UK services group Amey, started running the DLR on Sunday.
Serco, who held the franchise for 17 years from 1997, lost the £700m contract to Keolis in July.
Transport for London (TfL) said passengers would see a series of service improvements.
'Renationalisation call'
In a statement, TfL said: "This will mean cleaner trains and stations, more reliable lifts and escalators, more efficient and reliable station maintenance and faster passenger journeys.
"The network's current 99% reliability record will also be maintained - ensuring it remains one of the best performing railways in the UK."
But the ownership of the DLR was a concern for assistant general secretary of the RMT Steve Hedley.
He said: "The fact of the matter is that 70 out of 74 of our franchises now, on our railway network, have gone to foreign companies.
"We're not arguing that foreign capitalism is any worse than British capitalism, what we're arguing is that the 70% of the British people who want renationalisation should really be listened to."
Keolis already runs the Southeastern, Southern and London Midland rail franchises through its Govia joint venture with Go-Ahead Group.
