During the Middle Ages, a thriving center for learning and research was Muslim Spain, where students gathered to consult Arabic manuscripts of earlier scientific works and study with famous teachers. One of these teachers was Sa'id al-Andalusi, who in 1068 wrote Kitab Tabaqat al-'Umam, or "Book of the Categories of Nations," which recorded the contributions to science of all known nations. Today, it is one of few surviving medieval Spanish Muslim texts, and this is its first English translation.

Science ('ulum), as used by Sa'id and other scholars of that period, is a broad term covering virtually all aspects of human knowledge. After initial discussions of the categories of nations that did or did not cultivate science, Sa'id details the specific contribution of nine nations or peoples-India, Persia, Chaldea, Greece, Rome, Egypt, the Arab Orient, al-Andalus, and the Hebrews. He includes the names of many individual scientists and scholars and describes their various contributions to knowledge, making his book a significant work of reference as well as history.