A renowned poet, philosopher and traveller of the 11th century, Nasir-i Khusraw was also a major Ismaili thinker and author of the Iranian lands. His Ismaili writings, exclusively in Persian, have been preserved through the centuries by the Ismaili communities of the upper Oxus and Badakhshan, now situated in Tajikistan and Afghanistan. This is a study of Nasir-i Khusraw's life and aspects of his theological and philosophical thought in the context of his times. The author has devoted more than ten years of study to this subject, and includes in the book a detailed classification of Nasir's different genres of writings, and a summary of medieval as well as modern biographical studies.