In popular conception, Altaic is often assumed to constitute a language family, or perhaps a phylum, but in reality, it involves a historical, areal, and typological complex of five separate language families of different origins—Turkic, Mongolic, Tungusic, Koreanic, and Japonic—to which Uralic also adheres in the transcontinental context of Ural-Altaic. The similarities between the individual Altaic language families are due to prolonged contacts that have resulted in both lexical borrowing and structural interaction in a number of binary patterns. The historical homelands of the Altaic language families were located in continental Northeast Asia, but secondary expansions have subsequently brought these languages to most parts of northern and central Eurasia, including Anatolia and eastern Europe. The present review summarizes the basic facts concerning the Altaic language families, their common features, their patterns of interaction with each other and with other languages, and their historical and prehistorical context.