PIP: The effectiveness of medical practice is largely dependent on the quality of provider-patient communication. Inputs to the provider-patient encounter include prior experience with medical care, patient objectives for the visit, patient age, type of medical problem, the number of patient concerns, and characteristics of the physician's practice setting. Outcomes linked to the communication process include patient knowledge, provider-patient congruence on problems or recommendations, patient satisfaction, patient compliance with provider recommendations, and resolution of patient concerns or symptoms. The development of interactional analysis systems for the description of provider-patient communication processes in medical encounters should permit reasonably detailed descriptive research on these phenomena. Among the problems in this area have been the lack of a theoretical base for taxonomic categories of behavior, overlapping categories, the arcane nature of many disciplinary taxonomies, and lack of rigorous operational definitions for measurements. Given the rudimentary state of development of this field, descriptive designs for research will continue to be appropriate. However, interactional analysis systems will require additional development so that provider-patient encounters can be understood as episodes of information transfer through several channels. The development of hypotheses for experimental testing of efficacy of clinical strategies for communication requires measurement of pre to postencounter change.