The most comprehensive work of Weil is his Geschichte der Chalifen (5 vols., Heidelberg and Stuttgart, 1846–51), which is virtually an elaboration of the original works of Muslim historians, whom he in large part studied from manuscripts; it treats also of the Egyptian and Spanish califates. This was followed by the Geschichte der Islamischen Völker von Mohammed bis zur Zeit des Sultans Selim. (Stuttgart, 1866), an introduction to the medieval history of the Orient.
Weil's most comprehensive work is his "History of the Caliphs" (5 volumes, Heidelberg and Stuttgart, 1846–51), which is a substantial expansion of earlier Muslim historians' works, whom he primarily studied from manuscripts; it also covers the Egyptian and Spanish caliphates. His subsequent publication was "A History of Islamic Peoples from the Prophet Mohammed to the Time of Sultan Selim" (Stuttgart, 1866), an introduction to medieval history in the Orient.