This commentary is the fifth volume in a series of commentaries on the fourth-century historian Ammianus Marcellinus, which continues the commentaries by P. de Jonge on Books XIV-IXX. In XXIV the Persian expedition of Julian is described, from its successful start until the failure to take the capital Ctesiphon. The commentary deals both with the philological, literary and linguistic problems in the Latin text and with the historical and geographical details that are necessary for an understanding of the course of events. Special attention is given to the author s highly personal involvement as a participant in the expedition.