User interfaces and information systems have become increasingly social in recent years, aimed at supporting the decentralized, cooperative production and use of content. A theory that predicts the impact of interface and interaction designs on such factors as participation rates and knowledge discovery is likely to be useful. This paper reviews a variety of observed phenomena in social information foraging and sketches a framework extending Information Foraging Theory towards making predictions about the effects of diversity, interference, and cost-ofeffort on performance time, participation rates, and utility of discoveries. Author Keywords Social information foraging theory. ACM Classification Keywords H5.m. Information interfaces and presentation (e.g., HCI): Miscellaneous.