The Thoughtful Guide series is for serious spiritual seekers looking to deepen their knowledge of a particular region. It offers not primarily text books for the library, though they can be used as such, but accessible overviews of the history and the benefits that a particular religious practice can bring to the reader. The authors eschew fundamentalism and excessive simplifications, mapping out paths that can be followed with the mind as well as heart. Sufism is the heart of Islam. Its key is an inner light and awakening, an outer courtesy and service to humanity. It relates to Islam much as the mystical tradition does to Christianity, but far more prominently. With authors like Rumi achieving all-time popularity, Sufism is increasingly acknowledged as a spiritual answer to modern materialism. This introductory guide describes its origins and background, the relationship with Islam, and its spread throughout the world. It covers what it means to be a Sufi and the relevance of Sufism in modern life. Biographies of prominent Sufis and a selection of writing make this an indispensable guide to this profound tradition.