This Commentary seeks to elucidate the backgrounds and careers of the Emperors Galba, Otho and Vitellius, each of whom in succession briefly ruled the Roman Empire within the period June, A.D.68, to December, A.D.69. The origins and rise to prominence within the Roman state of the families of the Sulpicii Galbae, the Salvii Othones and the Vitellii are examined in detail and, in dealing with the individual Emperors themselves, an attempt has been made to assemble and comment upon virtually everything known about them. Within the period 68-69 the major concern has been with matters of chronology: the course of the revolt of Vindex in Gaul is analysed and a new timetable is proposed for events leading up to the battle of Vesontio; dates and a route are suggested for Galba's journey to and arrival in Rome; the background of the uprising of Vitellius is examined and the traditional account of this is destructively analysed; a detailed chronology is worked out for the latter part of the Principate of Otho and this, perhaps the most complex part of the thesis, seeks to incorporate and make sense of all of Otho's known actions in March-April, 69. The Vitellian invasion of Italy is examined in a similar manner and a framework is established for events up to Vitellius' arrival in Rome. In addition, the policies, appointments and relative success or failure of each of the Emperors are examined and commented upon. An attempt is also made to test certain current theories about the nature and interrelationships of the source materials underlying the extant accounts of this period.