Celebrations - including the town's annual carnival - will take place throughout the week.
This year's theme – New Elizabethan Age – has been chosen to commemorate the Queen's 90th birthday year.
Events will take place at venues throughout the week with the key highlight, as always, being the carnival on bank holiday Monday.
Mayor Marion Ross said: 'The festival's organisers are such an enthusiastic committee and they've put together a wonderful programme for 42nd festival.
'I particularly like that they've brought back some of the carnival traditions including the carnival king. queen, prince and princess.'
She added: 'I urge everyone to look at the programme and enjoy these community activities.'
Today, the festival's royalty will be chosen at a pageant ahead of Monday's parade, which will leave Heygates Mill at 12.15pm and travel through the town centre to the Howdale playing fields.
The festival officially starts tomorrow at noon during a French café event to celebrate the 40th anniversary of Downham Market's twinning with Civray, in France.
Other activities include a vehicle and pet show tomorrow afternoon; a Mamma Mia singalong on Thursday evening, a quiz night on Friday and a bingo evening which finishes the week on Saturday.
Coffee mornings, children's parties and a baby show have also been planned.
For more information search Downham Market Festival on Facebook.
Are you organising a community event? Email louise.hepburn@archant.co.uk
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