What is known is that Abu Yusuf became a close acquaintance of Abbasid caliph, Harun al-Rashid, who eventually granted him the title of Grand Qadi, or Qadi 'l-qudat; the first time such a title had been conferred upon someone in Islamic history. While at the time it was meant as an honorific title, the Caliph frequently consulted Abu Yusuf on legal matters and financial policy and even bestowed upon him the ability to appoint other Qadis in the empire. This made the position of Grand Qadi analogous to a modern-day chief justice. Abu Yusuf held the position of Grand Qadi until his death in 182/798CE. Literary works During his lifetime, Abu Yusuf created a number of literary works on a range of subjects including Islamic jurisprudence, international law, narrations of collected traditions (ahadith), and others. The Kitāb al-Fihrist, a bibliographic compilation of books written in the 10th century by Ibn al-Nadim, mentions numerous titles authored by Abu Yusuf. With one exception, none of these works listed in the Fihrist have survived. The exception is his book entitled Kitāb al-Kharāj, a treatise on taxation and financial issues facing the empire written at the request of the caliph, Harun al-Rashid. The Islamic empire was at the height of its power at the time of his writing and in his treatise, he sought to advise the caliph on how to appropriately conduct financial policies in accordance with religious law. While the caliph took some suggestions and ignored others, the overall effect was to limit the ruler's discretion over the tax system. A selection of other works credited to him that do not appear in the Fihrist have also survived. The Kitab al-Athar is a collection of Kufian traditions (ahadith) which he narrated. Kitab Ikhtilaf Abi Hanifa wa Ibn Abi Layla is a comparison of the opinions between the legal authorities, Abu Hanifa and Abu Layla. Kitab al-Radd ‘Ala Siyar al-Awza’i is a "reasoned refutation with broad systematic developments," of the opinions regarding the laws of war of the famous Syrian scholar, al-Awza’i. Some excerpts from his various other works that have not survived in their totality were incorporated in texts written by his disciples and were passed on through succeeding generations. For example, excerpts from Abu Yusuf's book, Kitabal-Hiyal (Book of Legal Devices) were incorporated in the book, Kitabal-Makharidj fi 'l-Hiyal written by his disciple, Muhammad al-Shaybani. Doctrine and Methodology As a disciple