Web services is the name for an important set of technologies for developing large-scale distributed systems, under the umbrella of Service-oriented architectures (SOA). Semantic Web services are building on top of Web services technology by describing various aspects of services using explicit, machine-understandable semantics that enables a certain degree of automation for various service related tasks. This lecture will give an overview of Semantic Web Services technologies. It starts by introducing the principles of Web and Service sciences along with the various technologies that are used by Web services. A set of Semantic Web Services frameworks, including both top-down and bottom-up approaches are then discusses. Finally an overview of applications of semantic technologies in service-oriented systems is provided.