Nominations for the award close on 4 November, with voting opening the following day. The winner will be announced at the organisation's awards dinner in December.
Members of the public can nominate their favourite green space and must explain in no more than 50 words what makes the space so special. One photo may also be uploaded. Each park may only be nominated once.
Once the top three parks have been finalised, those who nominated them will be invited to attend the Fields in Trust Awards ceremony at Lord's Cricket Ground on 2 December to see if your chosen park is the UK's best.
Fields in Trust will also be launching its revised Guidance for Outdoor Sport and Play: Beyond the Six Acre Standard at the House of Lords on 5 November.
The organisation was founded in 1925 as the National Playing Fields Association. It currently safeguards more than 2,500 sites, including playgrounds, playing fields, and formal and informal parkland across 28,000 acres of the UK.