Services are distinguished from products by their interactive nature, long-lasting business relationships among the engaged parties, and a gradual exchange of value over time. Today, An increasing portion of the world economy is represented by services instead of products. Thus, it is crucial to develop new methods for modeling, analyzing, and enacting service engagements that support the above distinguishing aspects of services. However, the current approaches are not suitable for the service-oriented economy because they offer only product-oriented abstractions. This monograph provides a technical framework with rigorous formal underpinnings to develop and maintain IT systems for service engagements. It has three main components: (1) a business-level method based on the notion of commitments for modeling services, (2) techniques for modeling and analysis of contracts via commitments, and (3) a method for systematically accommodating evolving business re­quirements. Beyond the scholarly impact, this work has influenced at least two practical efforts: standardization of foreign exchange pro­cesses under TWIST and study of business contracts under European Union IST-CONTRACT project.