The Thucydides Scholia are a body of explanatory notes, not the work of a single person. They are a collective compilation of annotations written in the margins and between the lines of manuscripts of the historian Thucydides. These notes were created, copied, and expanded over many centuries, from late antiquity through the Byzantine period, by generations of anonymous teachers, grammarians, and scribes.

Their creation began with the work of Hellenistic scholars, such as Didymus in the 1st century BCE, who wrote detailed commentaries. Later Byzantine scholars condensed, combined, and added to these notes, focusing on explaining Thucydides's difficult language and historical references. The scholia were preserved in medieval manuscripts and represent the accumulated teaching tradition surrounding this important author.

The notes themselves are categorized by modern scholars into different types and collections. Some offer older historical and linguistic explanations, while others provide more recent grammatical or rhetorical analysis. They are fragmentary and exist as scattered comments rather than a single, continuous text.

According to scholars, the Thucydides Scholia are significant for several reasons. They preserve fragments of lost ancient commentaries and show how Thucydides was studied for over a millennium. For editors today, the scholia are crucial for establishing the correct text of Thucydides, as they record ancient variant readings. They also provide a direct window into Byzantine education, illustrating how a complex classical text was taught and interpreted.