Strictly speaking, the history of comparative Indo-European studies begins in the late eighteenth century as a direct result of the momentous discovery that the ancient languages now classified as "Indo-European" (e.g., Latin, classical Greek, Sanskrit, Old English, Old Persian, Old Icelandic, Old Church Slavonic, Old Irish, Hittite, etc.) all stemmed ultimately from a common source, that is, Proto-Indo-European. As shall be seen, it soon became apparent that the speakers of these languages, which can be considered along with their progeny as members of a grand "family" of languages, shared more than simply a common linguistic heritage, and that among the most important features of this extralinguistic, Indo-European heritage was a common body of religious beliefs and practices.

To be sure, the taproots of the discipline can be traced back to classical antiquity, to the theories of Euhemerus (fl. 300 BCE) and other Greek and...