With an increasing amount of social interaction taking place in the digital domain, and often in public on-line settings, we are accumulating enormous amounts of data about phenomena that were once essentially invisible to us: the collective behavior and social interactions of hundreds of millions of people, recorded at unprecedented levels of scale and resolution. Analyzing this data computationally offers new insights into the design of on-line applications, as well as a new perspective on fundamental questions in the social sciences. We will review some of the basic issues around these developments; these include the problem of designing information systems in the presence of complex social feedback effects, and the emergence of a growing research interface between computing and the social sciences, facilitated by the availability of large new datasets on human interaction.