Modern languages like English, Spanish, Russian and Hindi as well as ancient languages like Greek, Latin and Sanskrit all belong to the Indo-European language family, which means that they all descend from a common ancestor. But how, more precisely, are the Indo-European languages related to each other? This book brings together pioneering research from a team of international scholars to address this fundamental question. It provides an introduction to linguistic subgrouping as well as offering comprehensive, systematic and up-to-date analyses of the ten main branches of the Indo-European language family: Anatolian, Tocharian, Italic, Celtic, Germanic, Greek, Armenian, Albanian, Indo-Iranian and Balto-Slavic. By highlighting that these branches are saliently different from each other, yet at the same time display striking similarities, the book demonstrates the early diversification of the Indo-European language family, spoken today by half the world's population. This title is also available as open access on Cambridge Core.