Corpus Juris Civilis
It is the basis of Latin jurisprudence (including ecclesiastical Canon law: ecclesia vivit lege romana) and a unique document about the life in Roman Empires at the time. It is a collection that gathers the many sources in which the leges (laws) and the other rules were expressed or published: proper laws, senatorial consults (senatus consulta), imperial decrees, case law, and jurists' opinions and interpretations (responsa prudentum).
The Corpus represented a true juridical revolution, organising Roman law into a convenient form and organic scheme, which foundationed the basis for all modern Civil Law (apart from obvious adaptions, such as those in Scottish law.)
The work was directed by Tribonian, a quaestor, and distributed in three parts: Digesto (or "Pandectae"), Institutiones, the Codex. A fourth part, the Novels (or "Novellae Constitutiones"), were added later.
It collects the roman imperial constitutiones mainly referring to those of the age of Hadrian, extracted by both the Codex Theodosianus and by private collections (among which the Codex Gregorianus and the Codex Hermogenianus). Due to the legal reforms by the same Justinian, this work needed to be updated, so a second edition of the Codex was issued in 534, after the Digesto.
Also called Pandectae, the Digesto was issued in 533, and contained the works of great Roman jurists, notably Ulpian, and some other sources (i.e. edicts). Intended as a solution for controversies in case law, it also records the law of Justinian's time.