A. E. Housman’s five-volume critical edition of Marcus Manilius’s Astronomicon has long been regarded as the definitive work on the subject. The task of bringing the edition together was one of considerable proportion which took Housman twenty-seven years to complete. It is now considered one of his most enduring and important contributions to scholarship. This volume contains the Latin text of the fourth book of Manilius, first published in 1920, and then reissued in a second edition by the Cambridge University Press in 1937. It offers a short note by A. S. F. Gow regarding the alterations, as well as a preface by Housman in which he elucidates three of the more challenging passages of verse.