Tube passengers have been promised new trains, track and signals, improved journey times and cleaner stations.
Greater frequency on the Central line is promised for next year.
The pledge came from the Metronet consortium which is to pour £17bn into London Underground (LU) over the next 30 years.
Metronet's takeover of the responsibility for the Bakerloo, Central and Victoria lines, has completed the government's controversial public-private partnership (PPP) of the network.
"We shall provide a safer, faster, cleaner and more reliable Underground," said Metronet chief executive Rod Hoare. "We will not fail."
But he warned passengers that improvements would take time, adding: "Making up for years of `make do and mend' will be no overnight task."
Rail unions, including the RMT, which have opposed the PPP, are vowing to carry on resistance to the plan.
8% journey time improvements on the Victoria line by 2005
47 new eight-car trains on the Victoria line, from 2009
190 new trains on the Metropolitan, Circle, Hammersmith & City and District lines from 2009
Refurbishment of existing District line trains, increased frequency on the Central line by 2004 and on the Bakerloo and Victoria lines in 2005
A 20% improvement in the service on the Waterloo & City line by 2006
A clean-up of all stations, with graffiti removed within 24 hours
A replacement of nearly all the track operated by Metronet as well as large-scale signalling improvements.
London mayor Ken Livingstone, whose Transport for London (TfL) agency will take control of the Tube, was also against the scheme.
Transport Secretary Alistair Darling said the deal was "good news for Londoners" and would mean £1bn investment a year for the next 15 years.
"I am now working towards a speedy and orderly transfer of London Underground to TfL," he said.
Paul Godier, managing director of LU, said: "This is the most momentous day for the Tube this century and follows five years of hard slog.
"At times, I thought it would never happen, but it has."
Responsibility for the rest of the Tube passed to another consortium, Tube Lines, which has promised to invest £4bn.
One of the features of the new-look Underground under Metronet will be trains with interconnecting gangways allowing passengers to walk through the entire train.