In this exhaustive survey of the institution of al-Kharaj - land tax in Islam - Ghaida Khazna Katbi provides a comprehensive and minutely detailed history of a practice which evolved from an exigency of conquest into an essential pillar of the early Islamic state. At the time of the Muslim conquests, al-Kharaj constituted a tax on lands owned by non-Muslims. It gradually developed into an instrument of state under 'Umar bin al-Khattab and reached its most refined and complex form under the Abbasids.Katbi provides a thoroughly documented statistical analysis of the historical materials for each region of the early Islamic world, in the process examining the Byzantine and Sasanian models which the Arab administrators consulted and in some instances adopted. She reveals unprecedented source material including never-before published correspondence from Umayyad functionaries as well as other documents from the Caliphate, Umayyad and Abbasid periods.