A semantic portal is a type of community information portal that exploits semantic Web standards (Berners-Lee, Hendler, & Lassila, 2001) to improve structure, extensibility, customization, and sustainability. They are similar to a traditional cyberspace portal, except that Web resources are indexed using a rich domain ontology (a specification of key domain concepts) as opposed to, for example, a list of keywords, and are based on new Web markup languages such as Resource Description Framework (RDF) (Manola & Miller, 2004) and Ontology Web Language (OWL) (McGuinness & Harmelen, 2004). RDF provides a flexible and extensible format for describing information items and associated metadata, while OWL supports explicit representation of the domain ontologies used to classify and structure the items. Together, these enable a more decentralized approach to portal architectures. This chapter discusses comprehensive, ontology-based approaches for building high-value semantic portals. State of the art development tools and techniques are first presented both from a client-side and server-side perspective. Next, widely used methodologies and tools for building ontologies are discussed. Finally, a tool called Ontoviews is demonstrated, which has been designed to assist semantic portal developers by providing accessibility to search and dynamic linking services.