The early period Ismaili jurist Al-Qādî al-Nu’mān appears as an important figure in the formation of Ismaili jurisprudence. There is very little information about Kadı Nu’mân’s family, childhood, education and intellectual environment. His full name is Abû Hanîfah Nu’man b. Muhammad b. Mansûr al-Qādî at-Tamîmî Al Qayrawānî. He was born around 290/903 (late 3rd (9th) century) into an educated family in Qayravan in North Africa. There are different opinions about the sect he belonged to when he was growing up. On the other hand, it is difficult to say for certain whether Nu’mān received education in the Ismaili sect due to the understanding of taqiyya in the madhhab. However, it is understood from the basic jurisprudence texts Nu’mān wrote that he most likely did not receive a Sunni education. Historians refer to him as ‘Qadi Nu’mān or Abu Hanifah al-Shi’i’ in order not to confuse him with the imam of the Hanafi school. Qādî Nu’mān served at different levels of the Fatimid State. Around 313/925, he entered the service of the first Fatimid caliph, Mahdi (r. 909-934 CE/297-322 AH), as a copyist and secretary. During the reigns of the third caliph Mansur and the fourth Fatimid caliph Mu’izz (d. 365/975), Qādî Nu’mān first served as a judge in Tripoli and then in Mansouriya, the Fatimid capital. After the Fatimids conquered Egypt and the center of government was moved to Cairo, Qādî Nu’mān was appointed by the fourth caliph Mu’izz as the head of the appellate courts (maẓālim). Qadi Numans career was at the peak in the period of Caliph Muiz. Qādî Nu’mān worked as a judge in the Fatimid State for about twenty-six years and continued this duty until his death in 363 (973). After the fall of the Fatimid caliphate, there haven’t been any other Fatimid or Ismaili jurists. Qādî Nu’mān is considered by contemporary Ismaili writers as a figure who systematically transformed Ismaili fiqh into an independent sect of fiqh. It can be said that Ismaili fiqh was developed through his works in the Fatimid period. His works continued as the main references in the fiqh studies and after the Fatimid period. With the death of Qādî Nu’mān, the period of ijtihad in Ismaili fiqh and its the establishment phase of Ismaili fiqh came to an end; The sect, in which esoteric interpretations were at the forefront, emerged as a distinctive school of fiqh by discarding ambiguity. Qādî Nu’mān was a very productive writer. He wrote important works related to the field of furu al-fiqh and usûl al-fiqh. Among his works, Ikhtilāf uṣūl al-madhāhib is undoubtedly one of the most important works in the early history of fiqh methodology. The work in question, which was originally written with the aim of rejecting the Sunni fiqh method, discusses the approaches of the Sunni schools of fiqh on ikhtilāf, taqlid, ijma, nazar, qiyas, istihsan, ijtihad and ra’y in a polemical manner. It reveals the differences of the Ismaili method from the Sunni method in terms of the sources on which the fiqh is based, the authority to make ijtihad and the theory of interpretation of the texts. Qādî Nu’mān examined the relationship between reason and revelation in general and the role of religious authority in comprehending and interpreting the texts while criticizing Sunni methods. Ikhtilāf uṣūl al-madhāhib has the characteristics of the works of development period as a form. It is possible to observe the question-answer and dialectic form which can be seen in the works of the development period throughout the work in question. Qādî Nu’mān endeavoured to persuade his opponents with a dialectical and argumentative style. Again, he replied to the Sunnis, who were his interlocutors, with their own proofs. In addition to these, Ikhtilāf uṣūl al-madhāhib has a unique feature in the matter of content. Because it is not very familiar to any Sunni handbook of usûl al-fiqh. It does not mention the hâss, âmm, ijma, qiyas, amir, nahy, alfaz bets, etc. The text is very similar to the Ahbari movement of the Jafari sect for it rejects all forms of ijtihad. It was written at a time when fiqh was not yet stable. Ikhtilāf uṣūl al-madhāhib gives us crucial information about the development of different usûl and fiqh sources in the middle of the fourth century. However, what is interesting here is that the information he gives about Ismaili method and fiqh is very little compared to the one about Sunni method and fiqh. Much of it centered on Sunni thought and its rejection. However, his ultimate goal was to defend the Ismaili doctrine. Ikhtilāf uṣūl al-madhāhib has shown us that Shiite works are as valuable as Sunni works in shedding light on the historical development of Sunni method of fiqh. The most important contribution of the work to fiqh is that it illuminates the early history of fiqh, the period of approximately one and a half centuries after Shafi’i’s death. In addition, it has been understood from the aforementioned work that the Sunni fiqh method is at an advanced level in terms of development in the early period.