What was initially described by Krahe as an Old European community based on studies of European hydronymy, and what has been described through comparative grammar as a North-West Indo-European dialect continuum - sharing common lexical and grammatical traits -, is now more clearly defined as an ancient Indo-European proto-language that expanded at least twice, from two small European regions during the third millennium: from the North Pontic steppe to the Carpathian basin in the first half, and from the Middle Danube to the rest of Europe in the second half. This book deals with that matter from a linguistic point of view and, as a consequence, with the reconstruction of different Proto-Indo-European stages and dialects, as well as neighbouring languages, including especially Uralic and its dialects.