Patrick Carnegie Simpson (1865–1947) was a Presbyterian churchman. After being ordained in 1895, he served in several towns in Scotland and England, notably Renfield Church, Glasgow, and Egremont, Wallasey before being appointed in 1914 to the Chair of Church History at Westminster College, Cambridge. During the period leading up to the Scottish Church Crisis (1900–1905), he worked closely with Principal Rainy, his former professor at New College, Edinburgh, in his efforts to secure the union of the Free and the United Presbyterian Churches. In the post-World War I period, he played a significant role in the area of inter-Church relations, particularly during the Lambeth Conversations and the Revised Prayer Book controversy. As an author, two of his books, and earned widespread acclaim.