The event, first held in 1954, was put up for sale at the beginning of July by the Hatchuel family, who ran the festival as a privately owned company.
The sale of the festival, which had operating profits of £7m this year, is reported to have come about after a disagreement between its owner and chairman, Roger Hatchuel, and his son, Romain.
Emap said the event would fit into its media operations -- which include the magazines Screen International, Broadcast and Media & Marketing Europe -- and that the acquisition would extend its core skills in event organisation, awards and exhibitions.
Derek Carter, chief executive of Emap Communications, said: "Working with the international advertising community, it is our intention to ensure the festival continues to reflect the rich diversity of this tremendously exciting market."
The Cannes festival was started by a group of cinema contractors, including Pearl & Dean. Inspired by the famous film festival, they wanted to celebrate the best of advertising and attract advertisers to their medium.
Romain Hatchuel had been expected to take over management of the festival from his 71-year-old father until two years ago, when he departed the company for a job at Euro RSCG.
He has since left the advertising network to set up a consultancy called The Key with the designer Philippe Starck.
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