I use perspectives derived from evolutionary theory, studies of complex systems, and developmental research to examine the dynamics and functions of long-term social relationships. I focus on social behavior in nonhuman animals, especially primates, wolves, and domestic dogs. Topics of interest include play, social reciprocity, cooperation, greetings, conflict resolution, emotions, and mood. I study the dynamics of social relationships by observing video-taped interactions in fine detail, using frame-by-frame and slow motion analysis. Questions being addressed include: How do other animals develop trusting relationships in the absence of spoken language? What do animals understand about the beliefs and intentions of their soical partners? How can understanding of nonhuman social relationships help us to better understand human behavior?