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Up to 40,000 people are expected at the Latitude Festival near Southwold in Suffolk over the weekend.
The music and arts event runs over four days until Sunday at Henham Park.
Among the headline music acts this year are Mumford & Sons, The 1975 and Fleet Foxes.
Performing on the Comedy Stage over the weekend are Dara O'Briain, Susan Calman, Katherine Ryan and Simon Amstell.
The Latitude Festival has been running since 2006 when the capacity was 15,000.
That has increased to nearly 40,000 over the years.
Latitude is still only a fraction of the 175,000 attendance at Glastonbury in Somerset and about half the size of the Reading and Leeds festivals.
It is promoted as a family event with many children attending with parents and there are even school visits.
Along with the music and comedy there are talks, science events and performance art.
Suffolk Police have been warning festival-goers to think about their safety and security.
While only a small number of incidents were reported to police in 2016 – mainly thefts - officers are keen to ensure crime on the site remains low again this year.
The main crime at music festivals across the UK tends to be thefts from tents on campsites.
The weather for the weekend event is expected to be rather cloudy but mainly dry with sunny spells and only the odd shower.
Temperatures will be around normal for the time of year peaking at 21-23°C.