Ach-Châfi'î is the founder of one of the four most renowned legal schools in the Muslim world, the Shafiite school. This work studies his youth, his culture, his teachers and his pupils, that is to say his life in general. He analyzes his century and his fiqh, his books, how they were composed and the confidence that can be placed in them. The sources of deductive reasoning that he used and the methods followed to develop his doctrine are also exposed, before moving on to the doctrine itself, its dissemination and the factors of its development. The author shows how ach-Châfi 'î, in interpreting the sources and subsidiary cases of the Shari'ah, sticks to apparent and general facts, refusing to consider conjectures and intentions, but analyzing concrete problems. Its ways are then the Koran, the Sunna and analogy. The fiqh of ash-Châfi'î perfectly represents the Islamic fiqh at the time of its blossoming and its maturity. It combines in a balanced way the fiqh of the mujtahids and that of the hadîth specialists. Ach-Châfi'î was the first to develop the science of the foundations of fiqh: fixing the criteria of analogy, attempting to define the rules of the Sunna and distinguishing the abrogated from the abrogating.