How and why are languages constantly changing? Historical lingustics seeks to find out by going beyond the history of individual languages to discover the general principles which underlie language change. But our evidence is severely limited. Most of the world's languages are still unwritten, and even in areas with long written traditions, such as Europe and the Near East, documentary evidence stretches only a little way back along the path of the historical development of languages. How, then, can we uncover our long linguistic prehistory, and what can it tell us about language change? This new textbook is an accessible general guide for students with an elementary knowledge of linguistics to the methods and theoretical bases of linguistic reconstruction, and of newer, less well established principles such as the application of linguistic universals and language typology, and quantitative techniques. Finally he reviews the principles for establishing language relationships and for uncovering information about the homelands and cultures of the prehistoric speakers of reconstructed languages.