This Festschrift in honor of Kurt R. Spillmann explores the complexity of human conflict and cooperation. Approaching the multi-faceted science of conflict from a wide range of disciplines and academic perspectives, the authors are renowned experts in their fields. Their contributions reflect the dynamics involved in any conflict, from the interpersonal to the international, and draw on the contributors' own evolutionary, psychological, cultural, ecological, and political theory backgrounds. The resulting publication is dedicated to the academic work of Kurt R. Spillmann, who, throughout his career, has promoted a holistic and transdisciplinary approach to the study of the most crucial topic of conflict research: the issue of us against them.