We live in a time unparalleled in human history: a time of fundamental cultural, political, social, and economic change marked by an exponential growth in human powers to electronically collect, process, store, retrieve and disseminate information and create new knowledge. The Handbook of Research on Social Interaction Technologies and Collaboration Software: Concepts and Trends focuses on the latest explosion of Internet-based collaboration tools and platforms reaching end-users; it explores their origins, structures, purposes, and functions; and it muses over how SIT can expand human abilities and powers. This broad spectrum of applications and services includes: online social networking, blogs, wikis, podcasts, web feeds, folksonomies, social bookmaking, photo and video sharing, discussion forums, virtual worlds, and mashups intended to advance interaction, collaboration, and sharing online.