The aim of this special section is to bring together leading research on computational models of affect-related phenomena in interactions occurring either in social media or agent-based systems, by attaining cross-fertilization between two relevant perspectives: on the one hand, research on agent architectures and cognitive models, mainly concerned with the integration of affective states into agents and open to the creation of virtual and embodied agents; on the other hand, research on techniques for sentiment analysis and opinion mining, mainly focused on the processing of affective information in social media, typically (but not only) expressed through text. The integration of models and methods between the two perspectives can open the way to the development of a new generation of social and interactive applications that leverage the affective dimension to promote improved, spontaneous technology mediated interactions, including human–computer and human–human interactions, on small and large scale. Our goal here is to provide an overview of the open research challenges for the community of researchers interested in analyzing and modeling the interplay between affect and interaction in agent-based systems and social media, as well as an introduction to the special section.