This book represents the culmination of the author’s work to date – it incorporates and updates previous articles and adds much new material. This book is not – nor was it ever intended to be – a comparative grammar of either the Indo-European or the Afroasiatic language families. It is, rather, a comparison of Proto-Indo-European with Proto-Afroasiatic. While this is not the first attempt to demonstrate that Proto-Indo-European and Proto-Afroasiatic are genetically related, it is the first to use the radical revision of the Proto-Indo-European consonantal system proposed by Thomas V. Gamkrelidze, Paul J. Hopper, and Vjačeslav V. Ivanov. Moreover, unlike previous endeavors, this is the first to make extensive use of data from the non-Semitic branches of Afroasiatic. The assumptions underlying this investigation of the possibility of the common genetic origin of Proto-Indo-European and Proto-Afroasiatic differ considerably from the assumptions made in other works on "Nostratic"; the methodological approach followed in this monograph has been one of rigorous adherence to the time-honored principles of comparative reconstruction.