In Chapter 1, we saw that the world's languages can be classified into language families, with the implication that all languages in a given family descend from a common ancestral language, or proto-language. In this chapter we turn to the most populous and one of the best-studied language families, namely the Indo-European language family.

Luckily for the study of Indo-European comparative linguistics, many of these languages have extremely old surviving written records: for example, the earliest records of Hittite go back to around 1,800 BCE; the earliest inscriptions in Mycenaean Greek date from 1,300 BCE; the oldest part of the Rigveda (written in an archaic dialect of Old Indic) probably goes back as far as 1,200 BCE; most ancient scriptures in Avestan, the liturgical language of Zoroastrianism, date from about 600 BCE; the Achaemenid Records in Old Persian are from about 500 to 400 BCE; and the oldest Latin inscriptions date from the sixth century BCE.