This volume, the ninth on Islamic material to be published in the Classics of Western Spirituality series, brings to light a highly significant but little known area of Islamic spirituality. Editor John Renard has assembled here a volume of texts, most translated here for the first time, culled from the great Sufi manuals of spirituality, on the theme of the complex and multi-faceted role of knowledge in relation to the spiritual life. He presents excerpts on knowledge from the works of nine major Muslim teachers, most translated from Arabic, but also including important texts from Persian originals. The Introduction offers a survey of the development of Sufi modes of knowing through the thirteenth century in their broader context, and then focuses on the manuals or compendia of Sufi spirituality treated here. Historical notes provide brief identifications of many of the individual sources and personalities mentioned throughout the treatises.