BBC: The first Night Tubes have rolled on to London Underground platforms – almost three years since the plan was first announced.
Trains will run on the Victoria and Central lines on Fridays and Saturdays.
The plan was announced in November 2013 and intended to begin in September 2015, but strikes over pay delayed the start by nearly another year.
Transport for London said there was a “huge demand” as passenger numbers on weekends had soared by 70% since 2000.
Night Tube services are expected to add £6.4bn to the London economy by 2030, creating 500,000 jobs, TfL said.
Trains will run every 10 minutes on the full Victoria line and on the Central line between White City and Leytonstone. They will run approximately every 20 minutes between Ealing Broadway and White City and between Leytonstone and Loughton/Hainault.
Unions staged a series of strikes during July and August last year before an agreement was finally reached in March 2016.
Before leaving office, the former mayor Boris Johnson, who had locked horns with the unions on ticket office closures and Night Tube plans, said he hoped services would get underway by July.
The new London Mayor Sadiq Khan was on the first Night Tube train on the Victoria line from Brixton.
Speaking ahead of the launch he said: “I’m really excited. Lots of people need to get to work late in the night or home from work – doctors, nurses, porters, security guards – but also it will be a massive boost to the night time economy.
“Think of the theatres, the live music venues, the restaurants. I’m really pleased and proud that finally the Night Tube is here.
“Boris Johnson deserves credit for talking about the Night Tube, but it was important to get the details right. I’m really pleased and proud that finally it’s going to happen.”
Night Tube timeline
November 2013: Night services are first announced by then-Mayor of London Boris Johnson
September 2014: It is announced that the first Night Tube services will begin in September 2015 – in time for the Rugby World Cup in England
September 2014: The Rail, Maritime and Transport (RMT) union warns that the plans have “not been properly thought through”
April and July 2015: Members of four unions take strike action over Night Tube proposals
September 2015: London Underground delays the start of the Night Tube until an agreement is reached
February 2016: RMT recommends acceptance of a pay and conditions deal
May 2016: New Mayor of London Sadiq Khan confirms that 24-hour trains will begin in August
August 2016: First Night Tube service begins.
The night service will be rolled out on the Jubilee, Piccadilly and Northern lines in the autumn.
There are also plans to expand the service to parts of the Metropolitan, Circle, District, and Hammersmith & City lines after modernisation and on parts of the London Overground in 2017 and the Docklands Light Railway by 2021.
Passengers will pay off-peak fares and day travelcards will be valid but will expire at 04:30.
About 100 police officers will be on patrol to allay any safety fears and eight new bus routes will now run 24-hour services to go hand-in-hand with the night services on the Tube.
