Matthew Blastares (Greek: Ματθαῖος Βλαστάρης or Βλάσταρις, romanized: Matthaios Blastares/Blastaris; fl. 1335–1346) was a 14th-century Byzantine Greek monk in Thessalonica and early scholarly opponent of reconciliation with Rome. He was also the writer of the Syntagma Canonum.

Blastares was a hieromonk in the monastery of Kyr Isaac in Thessalonica, where he died after 1346.^[1][2]

He is best known for his Syntagma kata stoicheion (lit. 'Alphabetical Treatise'), completed in 1335.^[1] The chief innovation of the Syntagma was Blastares' ambition was to reconcile canon law with civil law, whereas previous treatises had focused on one of the two, ignoring the other.^[1]

The Syntagma is subdivided into 24 sections, each on a specific legal topic, and usually further subdivided into chapters.^[1] It became very popular even outside the Byzantine Empire, and was translated into Serbian during the Serbian Empire of Stephen Dushan.^[1]

Apart from the Syntagma, Blastares was also the author of a number of other legal works, including a lexicon of Latin legal terms, and summaries of the nomocanons of Niketas of Heraclea, patriarchs Nikephoros I and John Nesteutes.^[2] His further work includes a poem on the offices and titles of the Byzantine court, a synopsis of rhetoric; theological treatises against the Latin Church, azymes, the Jews, and Palamism; a work on Divine Grace; a letter to Constantine II Lusignan on the Holy Spirit; as well as liturgical hymns and epigrams.^[2]

• Kazhdan, Alexander (1991). "Blastares, Matthew". In Kazhdan, Alexander (ed.). The Oxford Dictionary of Byzantium. Oxford and New York: Oxford University Press. p. 295. ISBN 0-19-504652-8.
• Trapp, Erich; Beyer, Hans-Veit; Walther, Rainer; Sturm-Schnabl, Katja; Kislinger, Ewald; Leontiadis, Ioannis; Kaplaneres, Sokrates (1976–1996). Prosopographisches Lexikon der Palaiologenzeit (in German). Vienna: Verlag der Österreichischen Akademie der Wissenschaften. ISBN 3-7001-3003-1.