Some of the roots of the characteristic negative attitude to homosexuality can be found in Peter Damian’s appeal to Pope Leo IX. Though written 900 years ago by an Italian monk in a remote corner of Italy, The Book of Gomorrah is relevant to contemporary discussion of homosexuality. The Book of Gomorrah asks the Pope to take steps to halt the spread of homosexual practices among the clergy. The first part outlines the various forms of homosexual practice, the specific abuses, and the inadequacy of traditional penitential penances, and demands that offenders be removed form their ecclesiastical positions. The second part is an impassioned plea to the offenders to repent of their ways, accept due penance, and cease from homosexual activity. Payer’s is the first translation of the full tract into any language from the original Latin. In his introduction to the tract Payer places The Book of Gomorrah in its context as the first major systematic treatise in the medieval West against various homosexual acts, provides a critique of Peter Damian’s arguments, and outlines his life. The annotated translation is followed by a translation of the letter of Pope Leo IX in reply to Damian’s Treatise, an extensive bibliography, and indexes. The book will be of interest to students of medieval history and religion, to ethicists and students of social mores, and to persons generally concerned with the historical roots of present-day attitudes to homosexuality.