Why are we social? Why most other animal species are? What are the pressures and benefits urging for social gatherings? And how are the necessary rules regulating social interactions built? Sociality and social interactions represent one of the most transversal topics in current research. The scientific approach of social interactions implies different theoretical and methodological perspectives, targeting the resolution of various complementary questions such as the causes of social behaviors, their dynamics, their development, their phylogenetic history, the attribution of social roles, and the modalities of synchronization and organization between individuals pursuing different or opposite goals, etc. This book gathers a set of contributions addressing the recent advances in the understanding of biological, neurological, psychological or socio-economic factors influencing social interactions in human and non-human (vertebrates and invertebrates) animals.