This book explores the relationships among four language families: Uralic, Yuk-agir, Chukchi-Kamachatkan, and Eskimo-Aleut (collectively referred to here as the Uralo-Siberian or US languages). While Fortescue is probably most widely known for his work on Eskimo-Aleut, he has worked with all of these languages to varying degrees, and so brings a deep knowledge of the material to this study.