This book is a comprehensive comparison of Proto-Indo-European, in all its stages of development and in all its aspects, with various other language families of Northern Eurasia, the Middle East, and the Indian subcontinent. It is an attempt to show that Proto-Indo-European is not genetically isolated but, rather, belongs to a larger linguistic grouping, namely, the Nostratic macrofamily. For the first time, all aspects of the putative proto-language are discussed in detail: phonology, morphology, vocabulary, syntax, and homelands. Copious references are given throughout to the relevant literature and the book ends with an English-Nostratic index. Also for the first time, a sizable amount of material has been included from Eskimo-Aleut and Chukchi-Kamchatkan. This book is, therefore, the most important contribution to Nostratic linguistics to appear to date.