Principles of Islamic Jurisprudence is one of the best-known textbooks written by the late Ayatullah Sayyid Muhammad Baqir al-Sadr (1934-1980). The current volume, the first in a three-volume series, is written in plain language to introduce beginners to the science of the principles of Islamic jurisprudence (usul). Originally entitled Durus fi 'Ilm al-Usul (Discourses on the Science of the Principles of Jurisprudence), but normally known as Halaqat al-Usul (Discourses on the Principles of Jurisprudence), the book was a revolutionary attempt at innovative and systematic presentation of the principles of Islamic jurisprudence. In the current volume, the late Ayatullah al-Sadr expounds on the discipline of usul and responds to the latest debates and challenges. It was no wonder that following its publication this work replaced other standard textbooks which had hitherto been used to teach the principles of jurisprudence.