This is the index volume to the monumental comparative grammar of the Indo-European languages published by Karl Brugmann (1849-1919) in the late-nineteenth century. It contains three indexes. The first, an index of words, is subdivided by language and organised so as to be useable as a comparative lexicon even by those unfamiliar with particular languages. It shows the huge variety of languages referred to in the book, from Pali and Venetic to Frisian and Old Cornish. The index of topics excludes categories such as individual sound changes that are easily located via the extensive tables of contents, but includes languages and dialects, grammatical and phonetic categories, and concepts such as place names and music. Finally, there is an index of names which will be of particular value to historians of the field and bibliographers.