The scholia to Thucydides, which are marginalia found in Medieval Greek manuscripts, provide us with the remainders of valuable ancient and Byzantine commentaries on the verbal and textual difficulties presented by Thucydides’s complex texts. The last edition of these scholia appeared in 1927, and this publication fails to live up to important contemporary requirements – namely, to base the text on the visual examination all of extant manuscript material and to winnow out the most valuable older textual elements from less important late-Byzantine supplements. The new edition meets both of these scholarly expectations in exemplary fashion.