Designed in 1726 by William Adam, the most important architect of mid-eighteenth century Scotland, Arniston was the first ‘country seat’ to be designed on the principles of Sir John Clerk of Penicuik, a key figure of the Scottish Enlightenment. Adam’s design enveloped and replaced an earlier 17th century mansion on the site of the tower house originally acquired by the family in 1571. The mansion was left unfinished from 1732 until 1753, when John Adam, William’s eldest son, completed it after re-arranging some of the rooms. Subsequent generations of the family added north and south porches and a new library, and altered the east pavilion. The house contains outstanding plasterwork by Joseph Enzer and many fine family portraits, and provides fascinating insights into three centuries of changing domestic arrangements. Our conservation plan provides a baseline of understanding the heritage and a strategy to ensure the house can continue to be used and enjoyed for years to come.