Enterprise ontologies (EOs), introduced in the mid 1990s, were expected to have a significant impact on enterprise computing, especially integration. However, despite a great deal of academic research on EOs, the actual use of EOs in real-life integration and planning projects is almost nonexisting. This paper describes an approach to build and use EOs for information system (IS) planning and integration projects with particular focus on real-life eBusiness applications. The approach is based on firsthand practical insights gained through construction and use of an IS planning and integration environment that needs to capture business processes, enterprise applications, integration technologies, and computer-communication platforms. The planning model with the aforementioned information is based on an EO and is populated by a set of intelligent advisors while they guide the users through various stages of the planning process. This ontology has been used to support over 40 real-life business scenarios in the telecom, manufacturing, financial services, retail, healthcare, and insurance industries. The practical contribution of this paper is that it connects ontologies to the practice of IS planning and integration, links ontologies to decisions such as enterprise application selection, and provides tools for automatically creating and maintaining ontology repositories.