The scientific study of human social interaction recently has undergone dramatic changes. Interpersonal behavior, like other natural phenomena, is being analyzed in ever-increasing detail. Just as the invention of the microscope permitted the identification of intricate physical processes, the recent development of sophisticated apparatus for the recording and analysis of social behavior has enabled the exploration of previously undetected interpersonal processes. While the behaviors involved in social interaction must be perceived at some level by the persons who are affected by them, they often are too complex in structure and too rapid in occurrence to be adequately recorded through direct observation. However, through detailed analysis of audio-visual records and with the aid of high-speed computers, the structures and functions of many fleeting interpersonal events now can be analyzed objectively and efficiently. Although such explorations still are in an early stage, some consensual discoveries are beginning to emerge. Thus, this is an opportune time to pull together some of the results of research, evaluate its progress and suggest promising directions for future study.