Cleonides was a Greek music theorist of the Roman imperial period, traditionally dated to the 2nd century CE, though some scholarship proposes a later date in the 3rd or 4th century. No biographical details of his life survive beyond the name transmitted in his work's manuscripts.

His sole extant work is the Eisagōgē harmonikē, or Introduction to Harmonics, a concise and systematic treatise summarizing the harmonic theory of Aristoxenus. Cleonides's significance rests entirely on this treatise, which became a primary and highly influential textbook for understanding Aristoxenian music theory. Its clarity ensured the transmission of core concepts—notes, intervals, scales, genera, and modulation—throughout the Byzantine and medieval Latin traditions.