Historical linguistics, also called diachronic linguistics, is the scientific study of language change over time. Principal concerns of historical linguistics include:

1. to describe and account for observed changes in particular languages
2. to reconstruct the pre-history of languages and to determine their relatedness, grouping them into language families (comparative linguistics)
3. to develop general theories about how and why language changes
4. to describe the history of speech communities
5. to study the history of words, i.e. etymology