The Language Grid is a distinctive language service infrastructure in the sense that it accommodates a wide variety of user needs, ranging from technical novices to experts; language resource consumers to language resource providers. As these language services are various in type and each of them can be idiosyncratic in many aspects, the service infrastructure has to address the issue of interoperability. A key to solve this issue is not only to build the services around standardized resources and interfaces, but also to establish a knowledge structure that copes effectively with a range of language services. Given this knowledge structure, referred to as a service ontology, each language service can be systematically classified and its usage specified by a corresponding API. This not only enables the utilization of existing language resources but facilitates the dissemination of newly created language resources as services.