The most widely accepted defining feature of the Semantic Web is machine-usable content. By this definition, the Semantic Web is already manifest in shopping agents that automatically access and use Web content to find the lowest air fares, or book prices. But where are the semantics? Most people regard the Semantic Web as a vision, not a reality—so shopping agents should not “count”. To use Web content, machines need to know what to do when they encounter it. This in turn, requires the machine to “know” what the content means (i.e. its semantics). The challenge of developing the Semantic Web is how to put this knowledge into the machine. The manner in which this is done is at the heart of the confusion about the Semantic Web.