London mayor Boris Johnson has said he hopes this weekend's Notting Hill Carnival will "help heal wounds" left by the recent riots.
Mr Johnson urged revellers to "let the true spirit of London shine through" at the annual event.
Scotland Yard will send 5,500 officers to west London on Sunday and then 6,500 will patrol the area on Monday.
The carnival will end 90 minutes earlier than in previous years in response to the recent disorder.
The change, which means the event coming to an end at 19:00 BST on both Sunday and Monday, followed concerns about safety from residents and businesses after the disturbances in the capital.
"It's right that the carnival goes ahead so we can show the world that the overwhelming majority of London's people are decent, law-abiding citizens who respect the law, love their city and want to celebrate our vibrant, diverse and historical culture," said Mr Johnson.
Metropolitan Police Commander Steve Rodhouse said intelligence received by the force suggested gangs wanted to "create trouble" at the parade.
But he said he was "really confident" that the large police presence - which will also include another 4,000 officers in parts of the city away from the carnival - would prevent any disorder.
One of the carnival's organisers Chris Boothman said he had been assured the "look and feel" of Scotland Yard's operation would be proportionate.
Mr Boothman, who is also a member of the Metropolitan Police Authority watchdog, said it was important to ensure there were enough officers "to give people confidence" without them "swamping" the streets.
Sometimes the Met had been referred to as "the biggest band in carnival", he said.
But those in charge of the operation had "a lot of experience" of policing the event, Mr Boothman said.
The parade, which runs through Ladbroke Grove, Westbourne Grove and Chepstow Road, is expected to attract hundreds of thousands of spectators.
There will also be nearly 40 "soundsystems", with DJs playing music during the day.
Transport for London has issued a guide to help people plan for the event, listing recommended travel routes and road closures.