Service-oriented architecture (SOA) promise to break former monolithic applications into pieces that can be distributed across several systems and that can even be offered by external service providers. With the loose coupling of services in combination with established standards, SOA enables dynamic, flexible applications which can always change rapidly by integrating new services as well as old legacy systems even across technological platforms as well as company boundaries. The development costs can be reduced significantly by reuse of services and by dynamic reconfiguration of service compositions. With the focus on B2B scenarios, new applications can easily be built by selecting and combining services. However, SOA approaches have also a high potential to improve the development of interactive applications, e. g. in business processes or B2C scenarios. But despite of this potential, the development of interactive applications, i. e. the development of corresponding user interfaces and its flexible combination together with functional services is not properly reflected in current Web Service standards and research approaches and thus, remains a major challenge and requires substantial development resources. Reasons are missing hints for user interface generation like description of parameter semantics and explicit UI descriptions that could be used to at least partially automate UI development and to select appropriate services in service repositories. Another challenge is the design of service interfaces appropriate for composing services and a correspondent UI for independently developed, autonomous interactive services. Methodologies are required that describe how to define services user interfaces and especially how to select the right granularity for such interfaces for reusing them in composed user interfaces.