A book on the principles of Islamic jurisprudence (Usul al-Fiqh) presented in a unique manner, as it combines the foundational principles of Usul, the secrets of Sharia, and the wisdom behind legislation. It is distinguished by its focus on the principles whose rationales were clarified by the Lawgiver, considering them as fundamental. It aims to reconcile reason and tradition through evidence, proofs, and examples.

The book comprises five sections:

First: On the scientific preliminaries of Fiqh and its principles.

Second: On the mandatory and subsidiary legal rulings (al-Ahkam al-Shar'iyyah al-Taklifiyyah wal-Wad'iyyah).

Third: On the objectives of Sharia (Maqasid al-Shari'ah) and related rulings.

Fourth: On legal evidence (al-Adillah al-Shar'iyyah) and the enumeration of legislative sources.

Fifth: On the rulings of independent legal reasoning (Ijtihad) and adherence to a school of thought (Taqlid), as well as conflict and preference (al-Ta'arud wal-Tarjih), and question and answer.

Al-Shatibi addressed topics that had not been explored before and dealt with subjects that no one had previously tackled.