Al-Kafi Ossoul is the title of the first of the three sections of the book Al-Kafi Hadith. In this section, hadiths related to Shiite beliefs and the lives of Shiite Imams and some hadiths that speak about the behavior of a Muslim are collected. Al-Kafi Ossoul is the most important source for understanding the beliefs of the Shiites, which has been published many times separately from the original Al-Kafi Book, and numerous translations and commentaries have been written and published on it. The author of the book Abu Ja'far Muhammad ibn Ya'qub ibn Ishaq Kolini Razi is known as the Trustee of Islam Kolini. He is one of the scholars and narrators of the period of minor absence. Al-Kafi Ossoul is the title of the first of the three sections of the book Al-Kafi Hadith. In this section, hadiths related to Shiite beliefs and the lives of Shiite Imams and some hadiths that speak about the behaviors of a Muslim are collected (3785 Hadith). In the other two parts of the book, the author deals with jurisprudential narrations and moral sermons. Al-Kafi Ossoul is the most important source for understanding the beliefs of the Shiites, which has been published many times separately from the original Al-Kafi Book, and numerous translations and commentaries have been written and published on it.