This study offers a comprehensive investigation into the institutional transformation of the praetorian prefecture from the Principate to the Late Roman Empire. Spanning the critical period from the reign of Carus to the death of Constantine (282–337 AD), the volume challenges traditional retrospective analyses by tracing the evolution of the office chronologically. It examines how the praetorian prefects transitioned from equestrian military commanders and members of the imperial comitatus into illustrious, powerful senatorial administrators at the head of vast regional districts. Through meticulous prosopographical analysis and the examination of epigraphic evidence—particularly the collegiate prefectural dedications—the author reconstructs the careers of individual prefects and the political contexts of their actions. Ultimately, the book illuminates how military crises, administrative reorganizations, and dynastic strategies shaped the definitive structural framework of the late antique regional prefecture.