The Institutes of Justinian is an anonymous 6th century law book. It provides foundations for civil and common law convention, with plenty of aspects still exhibited in modern legal philosophy.

The Institutes of Justinian ("Institutiones Justiniani" or "Justinian's Institutes") is a unit of the Corpus Juris Civilis, the sixth century codification of Roman law ordered by the emperor Justinian I. It is largely based upon the Institutes of Gaius , a Roman jurist of the second century A.D. The other units in the "Corpus Juris Civilis are: the Digest, the Codex Justinianus (Code of Justinian), and the Novellae Constitutiones ("New Constitutions" or "Novels"). Justinian's Institutes was one part of his effort to codify Roman law and to reform legal education, of which the Digest also was a part. Whereas the Digest was to be used by advanced law students, Justinian's Institutes was to be a textbook for new students. The need for a new text for first year students was addressed as early as 530 in the constitution "Deo auctore," where reference is made to something "...which may be promulgated to replace the elementary works, so that the raw intelligence of the student, nourished by a simple diet, may proceed more easily to advanced legal studies." Under the supervision of Tribonian, two law professors (Theophilus and Dorotheus) were assigned to extract statements about the basic institutions ("Institutiones") of Roman law from the teaching books created by writers of "authority" (as defined in the Law of Citations). The bulk of this new Institutes is the Institutes of Gaius, much of it taken verbatim; but it also uses material from the Institutes of Marcian, Florentinus, Ulpian, and perhaps Paulus (the other writers of "authority.". There is some debate over which of the commission members is responsible for what part of the new Institutes. Most recently it has been suggested that Theophilus and Dorotheus created the extracts from taken from the older works, while Tribonian revised and added new imperial laws. This new version of the Institutes was published on November 21, 533 and promulgated with the Digest on December 30, 533. These new Institutes were not only a textbook for first year law students, but, according to the decree that promulgated them (C. Tanta), they carried the force of law.[8] The Institutes of Justinian is arranged much like Gaius's work, being divided into four books covering "persons," "things,", and "actions." Unlike the Digest, the extracts do not provide inscriptions indicating from whom the original material was taken. First year law students used Justinian's Institutes as their textbook for centuries.[