Hephaestion (flourished 2nd century ad, Alexandria) was a Greek metrist, author of a work on metre in 48 books, which was reduced, by successive abridgments, to form a manual (Greek encheiridion). The manual became a popular school book, and it alone survives. It is the only complete ancient work on metrics extant. Appendixes dealing with poetic structure and with metrical notations may have been added by another hand.