Azo of Bologna or Azzo or Azolenus (fl. 1150–1230) was an influential Italian jurist and a member of the school of the so-called glossators. Born circa 1150 in Bologna, Azo studied under Joannes Bassianus and became professor of civil law at Bologna. He is sometimes known as Azo Soldanus, from his father's surname, and also Azzo Porcius (dei Porci), to distinguish him from later famous Italians named Azzo. He died circa 1250.
Azo wrote glosses on all parts of the Corpus Iuris Civilis. His most influential work is his Summa Codicis, a commentary of the civil law organized according to the order of Justinian's Code. The Summa Codicis, and Apparatus ad codicim, collected by his pupil, Alessandro de Santo Aegidio, and amended by Hugolinus and Odofredus, formed a methodical exposition of Roman law. As one of the very few medieval legal texts in Latin, the Summa Codicis has been translated into Old French.
Azo's works enjoyed great authority among generations of continental lawyers, such that it used to be said, Chi non ha Azzo, non vada al palazzo, roughly translated: "Who hasn't Azo on his side, will not go to court", neither as a plaintiff nor as judge. Azo's Summa Codicis, was also used (and often copied verbatim) by Henry Bracton in his account of English law. Azo's many glosses were ultimately incorporated into the Great Gloss of his pupil, Accursius.