The Mental Life of Monkeys and Apes: A Study of Ideational Behavior, has been considered important throughout human history. In an effort to ensure that this work is never lost, we have taken steps to secure its preservation by republishing this book in a modern format for both current and future generations. This complete book has been retyped, redesigned, and reformatted. Since these books are not scans of the authors' original publications, the text is readable and clear.