This code compiled, in the Latin language, all of the existing imperial constitutiones (imperial pronouncements having the force of law), back to the time of Hadrian. It used both the Codex Theodosianus and the fourth-century collections embodied in the Codex Gregorianus and Codex Hermogenianus, which provided the model for division into books that were divided into titles. These codices had developed authoritative standing.
Justinian gave orders to collect legal materials of various kinds into several new codes which became the basis of the revival of Roman law in the Middle Ages. This revived Roman law, in turn, became the foundation of law in all civil law jurisdictions. The provisions of the Corpus Juris Civilis also influenced the Canon Law of the church since it was said that ecclesia vivit lege romana — the church lives under Roman law.
The work was directed by Tribonian, an official in Justinian's court, and distributed in three parts: Digesta (or "Pandectae"), Institutiones, and the Codex Constitutionum. A fourth part, the Novels (or "Novellae Constitutiones"), was added later.
The Corpus Juris Civilis was composed and distributed in the Latin language, which was still the official language of the government of the Empire in 529-534 A.D., whereas the prevalent language of merchants, farmers, seamen, and other citizens was Greek. By the early 7th century, the official government language segued into the Greek under the lengthy reign of Heraclius (610-641).
The Code reflects the social order of the later Empire. The position of the emperor as an absolute monarch with unlimited legislative, executive and judicial power is implicit throughout.
Numerous provisions serve to secure the status of Orthodox Christianity as the state religion of the empire, uniting Church and state, and making anyone who was not connected to the Christian church a non-citizen.
The very first law in the Codex requires all persons under the jurisdiction of the Empire to hold the holy Orthodox (Christian) faith. This was primarily aimed against heresies such as Arianism. This text later became the springboard for discussions of international law, especially the question of just what persons are under the jurisdiction of a given state or legal system.
Other laws, while not aimed at pagan belief as such, forbid particular pagan practices. For example, it is provided that all persons present at a pagan sacrifice may be indicted as if for murder.
The principle of "Servitude of the Jews" (Servitus Judaeorum) was established by the new laws, and determined the status of Jews throughout the Empire for hundreds of years. The Jews were disadvantaged in a number of ways. Jews could not testify against Christians and were disqualified from holding a public office. Jewish civil and religious rights were restricted: "they shall enjoy no honors". The use of the Hebrew language in worship was forbidden. Shema Yisrael, sometimes considered the most important prayer in Judaism ("Hear, O Israel, the Lord is one") was banned, as a denial of the Trinity. A Jew who converted to Christianity was entitled to inherit his or her father's estate, to the exclusion of the still-Jewish brothers and sisters. The Emperor became an arbiter in internal Jewish affairs. Similar laws applied to the Samaritans.
The Digesta or Pandectae consist of a collection of legal writings mostly dating back to the second and third centuries. Fragments were taken out of various legal treatises and opinions and inserted in the Digest. In their original context, the statements of the law contained in these fragments were just private opinions of legal scholars. The Digest, however, was given the force of law, like the other parts of the Corpus Juris.
The Novellae consisted of new laws that were passed after 534. They were later re-worked into the Syntagma, a practical lawyer's edition, by Athanasios of Emesa between the years 572-77.
The merchant classes of Italian communes required law with a concept of equity and which covered situations inherent in urban life better than the primitive Germanic oral traditions. The provenance of the Code appealed to scholars who saw in the Holy Roman Empire a revival of venerable precedents from the classical heritage. The new class of lawyers staffed the bureaucracies that were beginning to be required by the princes of Europe. The University of Bologna, where Justinian's Code was first taught, remained the dominant centre for the study of law through the High Middle Ages.