The Sudanese Muslim reformer Mahmud Muhammad Taha (d. 1985) is known for his bold proposals for Islamic legal reform. The mystical theology underlying this reform, however, has been largely overlooked. This book analyzes Taha's Sufi-inspired modernist reform theology in its premodern and modern intellectual contexts. It argues that his unique reliance on premodern Sufi thought allows him to go beyond his contemporaries in bringing Islam into the modern age, in particular with his Islamic theory of evolution and his views on democratic governance and the rights of women and non-Muslims. Taha's theology can be viewed as a Sufi reply to both western secular thought and to the Salafi interpretations of Islam that have gained worldwide ascendancy in the past decades.