Shortly after Justinian became emperor in 527, he decided the empire's legal system needed repair. There existed three codices of imperial laws and other individual laws, many of which conflicted or were out of date. In February 528, Justinian created a ten-man commission to review these earlier compilations as well as individual laws, eliminate everything unnecessary or obsolete, make changes as it saw fit, and create a single compilation of imperial laws in force.

The Codex consists of twelve books: book 1 concerns ecclesiastical law, sources of law, and the duties of higher offices; books 2–8 cover private law; book 9 deals with crimes; and books 10–12 contain administrative law. The Code's structure is based on ancient classifications set out in the edictum perpetuum (perpetual edict), as is that of the Digest.