Higher Mental Functions of a Home-Raised Chimpanzee1 1The work described here was done at the Yerkes Laboratories of Primate Biology in Orange Park, Florida, between 1947 and 1954. Our subject, Viki, died of virus encephalitis in 1954 as she approached her seventh birthday. This report is offered now, essentially as written in 1956, because of the increased interest in anthropoid intellectual capacity induced by the work of the Gardners (see Chapter 3 of this volume), Premack (see Chapter 4 of this volume), and others. Our work was assisted by grants from the American Philosophical Society, the Samuel S. Fels Fund, and Grant M-669 from the National Institutes of Health, Public Health Service.