This thesis conducts a biographical study of Margaret Pole, Countess of Salisbury. Born in 1473, she was the daughter of George, Duke of Clarence, and niece of both Edward IV and Richard III. In 1541, at the age of 67, she was executed on the command of Henry VIII. Margaret's ancestry is detailed and her experiences under Edward IV and Richard III are noted. A study of her marriage is made which reveals the dynastic fears of Henry VII, while an understanding of the lineage and career of Margaret's husband, Sir Richard Pole, illustrates the importance that Henry VII attached to his half blood relatives. Margaret's restoration to the Earldom of Salisbury in 1512 is examined and the lands to which she was restored are specified. The change in lifestyle enjoyed by Margaret and her children is considered and the marriages of her three Sons and daughter, evaluated. Margaret's rare status as a peeress in her own right is explored. Her position as head of her family, as an independent member of the aristocracy, as 'good lord' and employer is analysed, the members of her affinity detailed and the role of her eldest son, Lord Montague, explained. The fall of the Pole family is investigated, which reveals that Henry Vill's action against them was not as unreasonable as some historians have maintained. The family's activities and the evidence against them is examined, while the relationship between Henry VIII and the Pole family is discussed. The significance of the international situation and extent and location of Margaret's lands is also highlighted. The thesis ends with an account of the countess's execution, and a brief note concerning the fate of those family members who survived the executions of 1538 and 1541.