Ripley breaks Europeans down into three primary categories: Teutonic, Alpine (Celtic), and Mediterranean. He uses skull size, skin color, height, and weight to determine these categorizations. A best seller, the book is hailed as "proof" of "Anglo-Saxon superiority."

Ripley warns of a complete submergence of Anglo-Saxons in America as they are "overwhelmed" by other Europeans and other races. He also highlights the tendency for city dwellers to be "darker" (i.e., not Anglo-Saxon), naming farms and the countryside as the places where most "pure" Anglo-Saxons reside.