In recent years, service-orientation has increasingly been adopted as one of the main approaches for developing complex distributed systems from reusable components called services. Realizing the potential benefits of this software engineering approach requires semiautomated and automated techniques as well as tools for searching or locating services, selecting the suitable ones, composing them into complex processes, resolving heterogeneity issues through process and data mediation, and reducing other tedious yet recurrent tasks with minimal manual effort. Just as semantics has brought significant benefits to search, integration, and analysis of data, it is also seen as a key to achieving a greater level of automation to service-orientation. This has led to research and development, as well as standardization efforts on Semantic Web Services. Activities related to Semantic Web Services have involved developing conceptual models or ontologies, algorithms, and engines that could support machines in semiautomatically or automatically discovering, selecting, composing, orchestrating, mediating, and executing services. This chapter provides an overview of the area after nearly a decade of research. The chapter presents the main principles and conceptual models proposed thus far, including OWL-S, Web Service Modeling Ontology (WSMO), and Semantic Annotations for WSDL (SAWSDL)/Managing End-to-End Operations-Semantics (METEOR-S), as well as recent approaches that provide lighter solutions and bring support for the increasingly popular Web APIs and RESTful services, like SA-REST, WSMO-Lite, and MicroWSMO. The chapter also describes the main engines and frameworks developed by the research community, including discovery engines, composition engines, and even integrated frameworks that are able to use these semantic descriptions of services to support some of the typical activities related to services and service-based applications. Next, the ideas and techniques described are illustrated through two use cases that integrate Semantic Web Services technologies within real-world applications. Finally, a set of key resources that would allow the reader to reach a greater understanding of the field is provided, and the main issues that will drive the future of Semantic Web Services (SWS) are outlined.