This chapter focuses exclusively on medieval Jewish civilization, from the fall of the Roman Empire to about 1492. It includes alphabetically organized entries, written by scholars from around the world, include biographies, countries, events, social history, and religious concepts. Ibn Adret was, without doubt, the greatest rabbinical authority of the Middle Ages, not only in Spain but throughout the world. One of the most interesting cases with which Ibn Adret had to deal concerned a Jewish informer, who apparently caused such danger for the entire Jewish community that an assembly of representatives of the communities of Catalonia, Aragon, and Valencia met to deal with him. One of the most famous works in Jewish history, known throughout the world and available in translations in many languages, is the "Guide of the Perplexed". Ibn Ezra composed commentaries on all of the books of the Bible, and in some cases in more than one recension.