According to its website:
The preservation for the benefit of the Nation of lands and tenements (including buildings) of beauty or historic interest and, as regards lands, for the preservation of their natural aspect, features and animal and plant life. Also the preservation of furniture, pictures and chattels of any description having national and historic or artistic interest.
The Trust was founded on 12 January 1895 by Octavia Hill (1838–1912), Robert Hunter (1844–1913) and Canon Hardwicke Rawnsley (1851–1920), prompted in part by the earlier success of Charles Eliot and the Kyrle Society. A fourth individual, the Duke of Westminster (1825–1899), is also referred to in many texts as being a principal contributor to the formation of the Trust.
In the early days the Trust was concerned primarily with protecting open spaces and a variety of threatened buildings; its first property was Alfriston Clergy House and its first nature reserve was Wicken Fen. Its first archaeological monument was White Barrow.
The Trust has been the beneficiary of numerous donations of both property and money. However, probably the most bizarre were those given by mysterious masked group known as Ferguson's Gang between about 1932 and 1940.
The focus on country houses and gardens which now comprise the majority of its most visited properties came about in the mid 20th century when it was realised that the private owners of many of these properties were no longer able to afford to maintain them. Many were donated to the Trust in lieu of death duties. The diarist James Lees-Milne is usually credited with playing a central role in the main phase of the Trust's country house acquisition programme, though he was in fact simply an employee of the Trust, and was carrying through policies which had already been decided by its governing body.
One of the biggest crises in the Trust's history erupted at the 1967 annual general meeting, when the leadership of the Trust was accused of being out of touch and placing too much emphasis on conserving country houses. In response, the Council asked Sir Henry Benson to chair an advisory Committee to review the structure of the trust. Following the publication of the Benson Report in 1968 much of the administration of the Trust was devolved to the regions.
In 2005 the Trust moved to a new head office in Swindon, Wiltshire. The building was constructed on an abandoned railway yard, and is intended as a model of brownfield renewal. It is named Heelis, which is the married name of writer Beatrix Potter, who was one of the National Trust's most important benefactors.
It was founded as a not-for-profit company in 1894 but was later re-incorporated by a private Act of Parliament, the National Trust Act 1907. Subsequent Acts of Parliament between 1919 and 1978 amended and extended the Trust's powers and remit. In 2005 the governance of the Trust was substantially changed under a Scheme made by the Charity Commission.
The Trust is governed by a 12-strong Board of Trustees. The Board is appointed and overseen by a Council which comprises 26 people elected by the members of the Trust, and 26 people appointed by other organisation whose work is related to that of the Trust, such as The Soil Association, the Royal Horticultural Society, and the Council for British Archaeology.
At an operational level the Trust is organised into regions which are aligned with the official local government regions. Its headquarters are in Swindon.
Expenses included £143.7 million for routine property running costs and £70.9 million for capital projects.
The Trust is heavily supported by volunteers, who numbered about 49,000 in 2006/07, contributing almost 3 million hours of work worth a notional £21.3 million.
At 28 February 2007 the Trust's investment fund was over £942 million, most of which is in tied funds which support specific properties and projects. This sum does not count the substantial value of the Trust's 'heritage assets' which are held inalienably, and so could not be realised even if the Trust wanted to. However, for insurance purposes those assets are valued at £5.7 billion.
The members elect half of the Council of the National Trust, and periodically (most recently in 2006) vote on the organisations which may appoint the other half of the Council. Members may also propose and vote on motions at the annual general meeting, although these are advisory and do not decide the policy of the Trust.
In the 1990s a dispute over whether stag hunting should be permitted on National Trust land caused bitter disputes within the organisation and was the subject of much debate at annual general meetings, but it did little to slow down the growth in member numbers.
There is a separate organisation called The Royal Oak Foundation for American supporters.
The Trust owns thousands of properties throughout England, Wales and Northern Ireland; including over two hundred mansion houses and gardens of outstanding interest and importance. The majority of these country houses contain collections of pictures, furniture, books, metalwork, ceramics and textiles that have remained in their historic context. Most of the houses also have important gardens attached to them, and the Trust also owns some important gardens not attached to a house. The properties include some of the most famous stately homes in the country and some of the key gardens in the history of British gardening.
The government of the United Kingdom has imposed inheritance taxes which often render intergenerational transfers of large estates impossible. This has proved a strong incentive for families to bequeath great houses to the Trust.
The Trust's land holdings account for more than 623,000 acres (970 square miles, 2520 km²), mostly of countryside, covering nearly 1.5% of the total land mass of England, Wales and Northern Ireland. A large proportion of this consists of the parks and agricultural estates attached to country houses, but there are also many countryside properties which were acquired specifically for their scenic or scientific value. The Trust owns or has covenant over about a quarter of the Lake District; it has similar control over about 12% of the Peak District National Park (See for example South Peak Estate, High Peak Estate). It owns or protects roughly one fifth of the coast in England, Wales and Northern Ireland (704 miles, 1126 km), and has a long-term campaign, Project Neptune, which seeks to acquire more.
The Acts also give the Trust the power to make bylaws to regulate the activities of people when on its land.
The 2007–08 annual report contains a list of all National Trust properties for which an admission charge is made that attracted more than 50,000 visitors in the year. The top ten were: