This volume features a collection of essays by primatologists, anthropologists, biologists, and psychologists who offer some answers to the question of what makes us human, i.e., what is the nature and width of the gap that separates us from other primates? The chapters of this volume summarize the latest research on core aspects of behavioral and cognitive traits that make humans such unusual animals. All contributors adopt an explicitly comparative approach, which is based on the premise that comparative studies of our closest biological relatives, the nonhuman primates, provide the logical foundation for identifying human universals as well as evidence for evolutionary continuity in our social behavior. Each of the chapters in this volume provides comparative analyses of relevant data from primates and humans, or pairs of chapters examine the same topic from a human or primatological perspective, respectively. Together, they cover six broad topics that are relevant to identifying potential human behavioral universals.