The resurgence of Islamic Civilization in the Near East in the 7th century AD and its expansion to Persian Empire and Westward provided opportunities of access Persian, Hellenic, and Roman writings in philosophy and medicine. Based on their observations and experiences, Islamic physician-philosophers expanded upon those writings and at times challenged them. Among these physician-philosophers admiring and challenging Galen was Zakariya Razi described as the greatest physician of Islam and Medieval Ages.A search of electronic and written materials about early Islamic Medicine was carried out focusing on Persian physician-philosophers Zakariya Razi. Abu Bakr Mohammad Ibn Zakariya al-Razi, known in the West as Rhazes, was born in 865 AD in the ancient city of Rey, Near Tehran. A musician during his youth he became an alchemist. He discovered alcohol and sulfuric acid. He classified substances as plants, organic, and inorganic. At age 30, he undertook the study of medicine. He was a prolific writer with more than 184 texts in medicine attributed to him with 40 of them currently available. Among them are Kitab al-Mansoori, Kitab al-Hawi, and Kitab al -Judari wa al-Hasabah. The latter is the first scientific description for the recognition and differentiation of smallpox and measles. The Bulletin of the World Health Organization of May 1970 pays tribute to Razi by stating "His writings on smallpox and measles show originality and accuracy, and his essay on infectious diseases was the first scientific treatise on the subject". Razi established qualifications and ethical standards for the practice of medicine. Zakariya Razi was not only one of the most important Persian physician-philosophers of his era, but for centuries his writings became fundamental teaching texts in European medical schools. Some important aspects of his contributions to medicine are reviewed.