The article aims at presenting the formal ontology CIDOC-Conceptual Reference Model, used for allowing information and documentation exchange and integration into the diverse sources of cultural heritage, and which is the leading ontology in the field since years. The ontology logical foundations are examined, entering into the details of the Description Logics, and also the theoretical configuration underlying the schema modelling. The relation (properties) structure - which is the ontology core - is presented along with the mechanisms proposed for the integration of cultural heritage information. In the end, this essays offers a brief and non-exhaustive overview of the information systems actually adopting the CIDOC-CRM ontology, from CLAROS to CulturaItalia.