Karl Brugmann (1849-1919) was professor of comparative language sciences at Freiburg im Breisgau when he began publishing his monumental, multi-volume comparative grammar of the Indo-European languages, synthesising the first 70 years of research in a rapidly developing academic subject, and identifying areas for future investigation. Volume 1, on phonology, begins with an introduction to Indo-European philology and provides a bibliographic orientation which is itself a fascinating snapshot of the field. The main part of the book focuses in turn on each Proto-Indo-European sound and its reflexes in the earliest attested languages of each language family (Sanskrit, Avestan, Armenian, Greek, Italic, Germanic, Old Irish, Balto-Slavic). Comparisons are also made within families, for example between Gothic and Old English. Brugmann also discusses Ablaut and sound changes including elision, contraction and lengthening as well as intonation and stress.