Catherine of Alexandria was undoubtedly one of the most popular saints in the Middle Ages. Her mystical union with Christ and her martyrdom ordeal inspired many works of prose and poetry in a wide variety of languages, including Italian. The Festa et storia is singular in that it is one of only two known medieval Italian plays about this saint, and it is structured to be performed over a three-day period. This religious play, or sacra rappresentazione, is analyzed in the context of medieval lay confraternities and of earlier treatments of Catherine's legend in Italy. The linguistic and literary aspects of the text reflect its place in the popular literary tradition of late medieval Siena. Also, the primary Latin source of the Festa et storia and many other Romance vernacular recensions, BHL 1663, is provided in English translation.