What precisely does Hilary's so-called Opus Historicum aim at? His Preface provides the clue. An introduction to the present edition sketches the mutilated work's discovery, tabulates its contents, and discusses problems of dating and authenticity. The English translation, which faces the Latin text, adopts some alternative readings. The Preface is elucidated in itself, and by reference to the earlier In Matthaeum. Central issues are hope and love, confessors and martyrs, imperial favours and threats, the bishop and his inner freedom. The circumspect treatment of both the reader and the subject reveals 'conscientization' of the bishops as the aim of the Opus Historicum. One of the book's excurses deals with the edict of Arles and Milan, and concludes that the nameless creed quoted by Hilary might preserve the lost edict's doctrinal preliminaries.