The Great Dorset Steam Fair (abbreviated GDSF, and since 2010 also known as The National Heritage Show) is an annual show featuring steam-powered vehicles and machinery. It now covers 600 acres (2.4 km2) and runs for five days. This used to be from the Wednesday after the UK August bank holiday, but from 2016 will be from the Wednesday before the Bank Holiday until the Bank Holiday itself. It is reputedly the largest collection of steam and vintage equipment to be seen anywhere in the world. The fair was founded by Michael Oliver, who died in 2009, and has been held in Dorset, England, every summer since 1969. The show is now run by Michael Oliver's son, Martin Oliver through Great Dorset Steam Fair Ltd.
Established in 1969, for the first 15 years of its existence the steam fair (then known as the 'Great Working of Steam Engines') was held at Stourpaine Bushes, then in 1985 it temporarily moved to nearby Everley Hill, as Bushes Farm were delayed in harvesting the crops from the fields used by the steam fair due to the weather conditions. In 1988, after 3 years at Everley Hill, where access by large crowds was difficult, it moved to its current permanent home at Tarrant Hinton, north of Blandford Forum, where access is vastly improved. The fair now attracts up to 200,000 visitors.
The most numerous exhibits are traction engines, tractors and farm machinery, but there are also sections for classic cars and commercial vehicles, working shire horses, rustic crafts, 'bygones' displays, and more. The show also has a market, autojumble, live music and funfair (some of which is powered by the steam engines). The funfair has traditional rides such as gallopers and steam boats, as well as modern ones like the "World Fair Wheel" which was sited in Manchester for the millennium. It is the biggest gathering of fairground organs in the UK.
The show regularly attracts around 200,000 visitors, and there can be 30,000 people on site, making the fair the fifth largest population centre in Dorset, after Bournemouth, Poole, Weymouth and Christchurch (the population of the historic town of Dorchester being only half that number).