In the commercial world, the value of ubiquitous computing applications is proportional to the range of business services that can be accessed in device-consumptive ways. Services originate in legacy applications of organizations, and are developed and operated typically in heterogeneous environments. Service-oriented architecture (SOA), supported by a complex stack of Web services standards, addresses ways in which software components of diverse applications can be homogeneously interacted with and composed. Thus, SOA provides a crucial mechanism for making services accessible to ubiquitous computing applications. In this chapter, we shed light on what SOA entails, based on Web services interfaces and messaging, and service composition through single-party process orchestration and multiparty choreography languages. For the latter, concrete patterns are used to describe the capabilities of prospective standards. Ways in which SOA needs be extended to allow wider and more flexible service trading, typified in current developments through service marketplaces, are then discussed. Such extensions, we argue, converge with directions in ubiquitous computing through so-called ubiquitous service networks and service ecosystems.