the comparative genetic study of the phonetics (phonology), morphophonemics, word formation, inflection, and sometimes the syntax of a family or group of related languages. A comparative grammar together with an etymological dictionary can summarize the results of the comparative genetic study of a family (group) of languages.

The first comparative grammars of the Indo-European languages were written by F. Bopp and A. Schleicher. A more complete comparative grammar of the Indo-European languages was written by K. Brugmann and B. Delbrück. Since the second half of the 19th century and throughout the 20th century, individual branches of the Indo-European family of languages and of other families and groups of languages have been the subject of comparative grammatical studies.