While reviewing all available anthropological literature on the native tribes of eastern Bolivia and western Matto Grosso for a sum-mary article for the Handbook of South American Indians, which is being prepared for the Smithsonian Institution, I became aware that the extent of the dataon these tribes would exceed the possible limits of the Handbook article. As much of the literature is in-accessible to research workers, several of the main sources being bibliographical rarities that are obtainable only in a few libraries, such as the Library of Yale University or the Library of Congress, and as the material had been assembled while preparing the sum-mary for the Handbook, it was obvious that it would be of great value to South American ethnology to condense in a single monograph everything which has been written on these Indians from the sixteenth century to the present day. Such a compilation is justified by the importance of the region and by the difficulty which anyone not having access to a large library would have in obtaining an idea of the ethnography of the area. For more than a century eastern Bolivia was the mythical" Tierra Rica" or" Eldorado" of which the Spanish conquerors dreamed. Today it may still be the Eldorado of anthropologists. Like aborig-inal California, theregion is peculiar in possessing an unusually large number of linguisticstocks. Within an area roughly bounded by the Cordillera, the Paraguay River, the Gran Chaco, and the upper Madeira River, we find thefollowing linguistic groups: Twpi-Guarani, Arawakan, Cariban, Takanan^ Panoan^ Chapakuran^ Ito-naman, Kayuvavan, Mosefenean, Lekoan, Yurakarean, Chiquiioan, Otukean, as weU as several languages of the upperGuapore River that are not yet classified, such as Huari, Guaratdgaja, Amniapa, etc. None of these languages has been recorded by a trained linguist some are known only through short word lists.