The term “Semantic Web” is often used more specifi­cally to refer to the formats and technologies that enable it . These technologies include the Resource Description Framework (RDF), a variety of data substitution formats, and notations such as RDF Schema and the Web Ontology Language, all of which are intended to provide a formal description of concepts, terms, and relationships within a given knowl­edge domain. In the last decade the increasing popularity of the World Wide Web has lead to an exponential growth in the number of pages available on the Web. This huge number of Web pages makes it increasingly difficult for users to send required information. To enable machines to support the user in solving information problems, the Semantic Web proposes an extension to the existing Web that makes the semantics of the Web pages machine process able. The Semantic Web is well recognized as an effective infrastructure to enhance visibility of knowledge on the Web. The foundation of the Semantic Web is ontology , which is used to unambiguously represent our conceptualizations. Ontology engineering in the Semantic Web is primarily supported by languages such as RDF, RDFS and OWL. This article discusses the requirements of ontology’s in the context of the Web, compares the above three languages with existing knowledge representation formalisms, and surveys tools for managing and applying ontology’s.