In this thesis, we present a theory of value for the design and analysis of service ecosystems. The theory is based on general systems thinking. The concept of a system is used for relating knowledge from different disciplines (such as software engineering, requirements engineering, conceptual modeling, economics, service-oriented computing, and philosophy) to the domain of service ecosystems. The proposed definition of value is an input or an output that helps a system to construct and to maintain an identity for an observer. This definition is used to design and analyze service ecosystems through the prism of the value that systems find in participating in service ecosystems. The theory is constructed on the two following ideas: (i) the reflections, resulting from a collaboration with industry partners, on the role of the concept of value in the design and analysis of an information system for integration in an organization and (ii) on a review of the state of value definitions and theories in the academic context. The use of multiple methodologies for system design and analysis, which we observe in service ecosystem design, introduces another question: How do we connect different system representations? To this end, this work contributes a set of heuristics for the reconciliation of methodologies. Instead of asking the question of "How can we align and connect all knowledge from one methodology to the other?", the reconciliation heuristics are based on the assumption that this is neither necessary, nor possible. Accepting that the reconciliation is a continuous process and guiding it, with the help of the heuristics, is a technique for relating, converging, and enabling the independent existence of the knowledge to be modeled via different methodologies. We conclude the thesis with our current inquiries about the application of the value and reconciliation principles in the domains of services and privacy. We propose definitions for both services and privacy and offer a future research agenda for the further research and practical development of the theory of value.