The De Officiis (`On Duties'), written hurriedly not long before Cicero's death, has always commanded attention. It is based on the moral philosophy of the Greek Stoic Panaetius; but Cicero adapted the material to his audience in such a way that the book stands as an invaluable witness to Roman attitudes and behaviour. This new edition is based on a more systematic examination of the vast manuscript tradition than has previously been attempted, and exploits fresh evidence for the poorly represented X branch. The apparatus shows with new clarity the major contribution to the emendation of the text made by scribes and readers of the later manuscripts, both in the Middle Ages and in the Renaissance.