This paper aims to bridge the gap between ontological art and ontological engineering by providing a structured methodology for building ontologies from scratch. The authors, Mariano Fernández, Asunción Gómez-Pérez, and Natalia Juristo, from the Laboratorio de Inteligencia Artificial at the Universidad Politécnica de Madrid, outline a set of activities, techniques, and deliverables for the ontology development process. They propose an evolving prototype life cycle, which includes specification, conceptualization, formalization, integration, implementation, and maintenance, allowing for flexibility and adaptability throughout the development process. METHONTOLOGY, a well-structured methodology, is introduced, detailing each phase and the techniques to be used. The paper also emphasizes the importance of knowledge acquisition, documentation, and evaluation, and recommends the reuse of existing ontologies to streamline the process. The authors draw on their experience in developing an ontology for the chemical domain to support their methodology.This paper aims to bridge the gap between ontological art and ontological engineering by providing a structured methodology for building ontologies from scratch. The authors, Mariano Fernández, Asunción Gómez-Pérez, and Natalia Juristo, from the Laboratorio de Inteligencia Artificial at the Universidad Politécnica de Madrid, outline a set of activities, techniques, and deliverables for the ontology development process. They propose an evolving prototype life cycle, which includes specification, conceptualization, formalization, integration, implementation, and maintenance, allowing for flexibility and adaptability throughout the development process. METHONTOLOGY, a well-structured methodology, is introduced, detailing each phase and the techniques to be used. The paper also emphasizes the importance of knowledge acquisition, documentation, and evaluation, and recommends the reuse of existing ontologies to streamline the process. The authors draw on their experience in developing an ontology for the chemical domain to support their methodology.