This book, now back in print having been unavailable for many years, is one of the most important contributions to Turkic and Mongolic linguistics, and to the contentious 'Altaic theory'. Proponents of the theory hold that Turkish is part of the Altaic family, and that Turkish accordingly exists in parallel with Mongolic and Tungusic-Manchu. Whatever the truth of this theory, Gerard Clauson's erudite and vigorously expressed views, based as they were on a remarkable knowledge of the lexicon of the Altaic languages and his outstanding work in the field of Turkish lexicography, continues to command respect and deserve attention.