Byzantinism, or Byzantism, is the political system and culture of the Byzantine Empire, and its spiritual successors the Orthodox Christian Balkan countries of Greece and Bulgaria especially, and to a lesser extent Serbia and some other Orthodox countries in Eastern Europe like Belarus, Georgia, Russia and Ukraine. The term byzantinism itself was coined in the 19th century. The term has primarily negative associations, implying complexity and autocracy.

This negative reputation stressed the confusing complexities of the Empire's ministries and the elaborateness of its court ceremonies. Likewise, the "Byzantine system" also suggests a penchant for intrigue, plots and assassinations and an overall unstable political state of affairs. The term has been criticized by modern scholars for being a generalization that is not very representative of the reality of the Byzantine aristocracy and bureaucracy.