In this paper we report on the study of composite interface failure processes using quantitative acoustic emission (AE) measurements. The destruction of model composite specimens is studied in order to isolate the constituent interactions. A number of previous fiber pullout studies of composite interface failure have relied on fiber force and displacement data to elucidate fiber/matrix properties. In our study, we use ultrasonic waves that emanate from the failure region to determine the forces that are released as the interface fails. We avoid assuming a specific model for the micro-processes; rather, the forces are determined directly from the acoustic emission signal detected at a distance from the source.