Multi-market contact can either escalate or deescalate rivalry. Recent empirical work has revealed an inverted U-shaped relationship between multi-market contact and rivalry. These findings have lead many to suggest that mutual forbearance (MF), a switch from competition to cooperation across markets, is a natural outcome of increasing multi-market contact between two firms. Despite the relatively widespread acceptance of this suggestion, we do not have a theoretically grounded explanation for how this switch from rivalry to mutual forbearance occurs. This dissertation takes up this task. Theories of learning and trust are used as the grounding for the development of a theoretical model of the process by which multi-market rivals switch from competition to cooperation across markets. The model is tested using data from the U.S. Scheduled Passenger Airline Industry. Results support the general theoretical foundations of the model and provide new insights into the genesis of mutual forbearance.