Mommsen's influential study (1871–1888) is a systematic treatment of the workings of the Roman state. The renowned German scholar proposed an original and sometimes controversial understanding of Roman institutions, based around the categories of nineteenth-century constitutional law. This volume focuses on the Principate and the imperial household.

Theodor Mommsen's influential multi-volume work, first published between 1871 and 1888, is a systematic treatment of the intricate workings of the Roman state. The renowned German scholar proposed an original and sometimes controversial understanding of Roman institutions, based around the categories of nineteenth-century constitutional law. The Romans themselves never actually codified their complicated body of law, but by applying a historical approach to describe the development of Roman law Mommsen succeeds in making it more accessible to the reader. He systematises the many diverse legal elements upon which the Roman constitution was based and offers a coherent reading of it. In Volume 2, Part 2 Mommsen explains the origins and development of the Principate (the office of the Roman emperor), and describes the role of the imperial household. He also covers the tribunal court and the institutions responsible for governing Rome and Italy.