The "epidemiology of knowledge" underlying clinical decision making related to antibiotic therapy is one of the most important determinants of how such therapy is used, misused, or not used. A growing literature describes how prescribers and patients acquire the information that influences them in their utilization of these agents. The quality and content of this information ultimately determine whether a given microorganism will ever meet a particular drug. Most evidence indicates that there is considerable room for improvement in such decision making. Research data, including those from randomized controlled trials, have been used to compare the efficacy of several methods of improving the flow of information about proper antibiotic use. While traditional passive forms of education are not powerful means of changing prescribing behavior, innovative approaches, including person-to-person tutorials, can improve the quality of antibiotic prescribing. Benefit-cost analysis documents that these programs can save more than they cost. Additional research on these questions will be a powerful way of maximizing both effectiveness and efficiency in the treatment of infectious diseases.