The Ikhwan Al- Safa' or Brethren of Purity were a highly secretive group of tenth-century Shi'ite thinkers, their identities remaining unclear even today. Renowned for creating the legendary Rasa'il Ikhwan al-Safa, an encyclopedia of philosophical sciences, they proposed a coherent intellectual system that sought to reconcile human reasoning with prophetic revelation. This fascinating survey provides a clear, objective and innovative introduction to the Brethren of Purity and their encyclopedic project, showing its critical place in the history of Arabic science, philosophy and literature.