Information push and information pull have recently emerged as useful concepts to describe the operation of distributed information resources. Information push, in particular, is becoming closely associated with intelligent agent functionality. Loosely speaking, if a user requests and receives a very speci c piece of information, this is information pull. If information is sent i n anticipation of the user's need, or the agent's response includes information not directly solicited, then the

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... ation is characterized as information push. Intuitively, junk mail electronic or paper, television newscasts and wirefeeds are examples of information push. New web services such a s P ointcast and Informant are examples of more selective push technologies. Web browsing, library searches, and telephone white pages are traditional examples of information pull. Clearly, these categorizations can be ambiguous and are easily lost in semantics. The main goal of this paper is to formalize these concepts and describe a mathematical framework around which further work can be more precise. Speci cally, w e develop a stochastic framework based on Markov models to describe an ambient e n vironment and an agent system. Depending on the relationships between the environment, the agent and the user's performance criterion, a continuum of possible information push and pull scenarios can be described. Some basic analytic results concerning the operation of a push pull information system are derived.