The agent-based approach is an effective one for building middleware interconnecting distributed heterogeneous resources and providing semantic interoperability among them. On the other hand, agents need the Semantic Web technologies for flexible yet effective coordination among them with a particular issue of enabling agents to communicate not only about the domain but also about their own abilities, goals, and present and intended actions. This paper describes Semantic Agent Programming Language (SAPL)intended to be a core middleware language for the Semantic Web. S-APL integrates the semantic description ofthe domain resources with the semantic prescription of the agents' behaviors. Additionally, S-APL can be used as the content language in the inter-agent communications, both in querying for data and in requesting for action.