As humans appear to be literally wired for social interaction, it is not surprising to observe that social aspects of human behavior and psychology attract interest in the computing community as well. The gap between social animal and unsocial machine was tolerable when computers were nothing else than improved versions of old tools (e.g., word processors replacing typewriters), but nowadays computers go far beyond that simple role. Today, computers are the natural means for a wide spectrum of new, inherently social, activities like remote communication, distance learning, online gaming, social networking, information seeking and sharing, training in virtual worlds, etc. In this new context, computers must integrate human-human interaction as seamlessly as possible and deal effectively with spontaneous social behaviors of their users. In concise terms, computers need to become socially intelligent.