In this book a semantic service discovery model is presented focusing mainly on services provided and accessed by mobile devices. The proposed model aims to improve the technology of the current service discovery models which are mostly based on syntactic descriptions of the services. In addition we are concerned about maintaining an architecture that uses market standards and is light enough to run on devices with limited resources. To achieve these goals we use Semantic Web Services. The services are described through ontologies in which we can define concepts and determine relationships between them.