Over the past few years a new kind of application, the "recommender system", has appeared, based on a synthesis of ideas from artificial intelligence, human-computer interaction, sociology, information retrieval, and the technology of the WWW. Recommender systems assist and augment the natural process of relying on friends, colleagues, publications, and other sources to make the choices that arise in everyday life. Examples of the kinds of questions that could be answered by a recommender system include: What kind of car should I buy? What web-pages would I find most interesting? What people in my company would be best assigned to a particular project team?