Events during the month will include a Tudor river pageant
Londoners are being urged to get out and explore their surroundings in a month-long celebration of the city.
Taking place throughout June, the Story of London consists of more than 350 events and activities covering history, design, music, theatre and film.
It aims to offer new experiences and insights into London, historically, culturally and socially.
The festival was officially launched by mayor Boris Johnson at the Tower of London on Wednesday.
He was joined by the chairman of the London Committee for the Heritage Lottery Fund, Wesley Kerr.
Mr Johnson said: "London. Londinium amo. A little place by the river that is home to millions and is a colossus on the world stage.
"There are so many stories to tell, in so many different ways, and the Story of London will be a kaleidoscopic exposition of the city's past, present and future."
The first major event is on Friday, as choirs across the city take part in a musical call to action.
On Saturday, curators at the Museum of London are presenting an event which looks at 1,000 years of city history in one day.
Historic Royal Palaces are also organising a "spectacular" Tudor river pageant to mark the 500th anniversary of King Henry VIII's coronation.