The Aristotle Collection of the University of Pennsylvania Library owes its existence to Dr. Charles W. Burr, Professor in the University's Medical School and generous donor to the library. His gifts of books over a long period of years included any valuable Aristotle items and in 1932 he presented his own library to the University. A bequest at his death in 1944 established a fund which has enabled the library to purchase a number of important additions to the collection. These books and manuscripts are a rich source for those interested in medieval and Renaissance scholarship. The very number of the early printed editions in this catalogue-over five hundred-attests to the importance that was attached to the study of Aristotle during the fifteenth, sixteenth, and even the seventeenth centuries. Medieval Latin translations of the texts of Aristotle continued to appear during the Renaissance. The twelfth-century translations of Guilelmus of Moerbeke can be noted in this catalogue as late as 1589; even when a contemporary translation was available and was used, it was not uncommon for the earlier version to be printed with it. The list of commentators, translators, and editors of the Aristotelian tradition includes the names of many well-known humanists from all over the continent. These men, protagonists of the new learning, nevertheless concerned themselves with that same philosopher who so dominated the teachings of the medieval schools. Another indication of the Aristotelian influence is the great number of translations of his works into the vernacular. The German, Italian, and French versions in this collection, as well as in others, attest to the wide interest in his works in Europe. Few aspect of medieval and Renaissance civilization were free from the influence of "The Philosopher" and this work is therefore a valuable adjunct to any study of the period. The collection, seemingly so strictly limited to one great figure, will prove useful in a great variety of scholarly pursuits.