With the advancement of Service-Oriented Architecture in the technical and business domain, the management & engineering of services requires a thorough and systematic understanding of the ser-vice lifecycle for both business and software services. However, while service-oriented approaches acknowledge the importance of the service ecosystem, service lifecycle models are typically internally focused, paying limited attention to processes related to offering services to or using services from other actors. In this paper, we address this need by discussing the relations between a comprehensive service lifecycle approach for service management & engineering and the sourcing & purchasing of services. In particular we pay attention to the similarities and differences between sourcing business and software services, the alignment between service management & engineering and sourcing & purchasing, the role of sourcing in the transformation of an organization towards a service-oriented paradigm, the role of architectural approaches to sourcing in this transformation, and the sourcing of specific services at different levels of granularity.