Thirty years ago Robert Kaster’s Guardians of Language: The Grammarian and Society in Late Antiquity (1988) investigated ancient Greco-Roman grammarians as social agents within their social and cultural context. This collection of twelve essays develops that line of inquiry by focusing on one dimension of their activity: how Roman grammarians—as well as scholars and intellectuals more broadly—described, made sense of, and resisted linguistic diversity within the Roman Republic and Empire. This includes social and diachronic variety within Latin as well as multilingual contact with Greek and other Mediterranean languages. The essays cover five centuries of Latin reflection on language, from Varro to the fifth or sixth century CE. The book concludes with an autobiographical Epilogue by Robert Kaster about the origins of Guardians of Language and updates to the prosopography of known ancient grammarians found in Guardians.