Service-oriented architectures (SOA) aim to define a common approach for both the providers and consumers of services by introducing the mechanisms necessary to publish services, to search for services, and to request the execution of services. The proliferation of the providers of services offering identical or similar services has led customers to choose services based on information behind their functionality. This type of information may regard issues such as quality, performance, response time, security, availability, and reliability. In the scientific literature, such information is known under the name of non-functional properties or non-functional requirements. Usually, non-functional requirements are not explicitly addressed during the analysis and design of Information Systems, even if they are fundamental for the architectural or technological decisions. Hence, they are neither traceable nor documented. However, in recent years, the engineering of non-functional properties together with the functional ones is gaining more and more the attention of software engineers. There are various proposals for the specification of non-functional features which range from informal textual specification to extensions of the Unified Modelling Language. The aim of this chapter is to provide an overview on non-functional issues in service oriented architectures. First, it introduces the non-functional requirements which should be addressed in service-oriented architectures and the challenging issues they raise (i.e., specification, conflicts, run-time management). Second, it presents the available approaches related to the engineering of non-functional issues. Third, it discusses the possible future trends regarding this topic. © 2011, IGI Global.