With its range focused on Indo-European and extending across Eurasia and into the Americas, this collection of seventeen studies investigates various aspects of the long-range comparison and classification of Indo-European and other major language groups. Some of them confront the controversial question of whether Indo-European and certain other language families had, extending the celebrated phrase of Sir William Jones in 1786, 'sprung from some common source'. With comparative linguistics of recent decades in danger of stifling from an excess of caution, the quest for the answer to that question has now been broadened to attempt to find a deeper common source than Proto-Indo-European. This volume surveys the progress of the genetic classification of languages over the years, records recent developments, and points to abundant opportunities for future research. The contributors - some of the world's leading investigators of the genetic classification of languages - have adopted a broad outlook, looking beyond comparative Indo-European linguistics in two ways: