The present document contains the specification of the oneM2M base ontology. A formal OWL representation of the base ontology can be found at http://www.onem2m.org/ontology/Base_Ontology. The present document also specifies an instantiation of the base ontology in oneM2M resources which is required for generic interworking. In addition the present document contains the functional specification for an Interworking Proxy Application Entity (IPE)@ the oneM2M resources and their usage for generic interworking. Finally an example is given how external ontologies can be mapped to the base ontology. The example uses the Smart Appliances REFerence (SAREF) ontology (http://ontology.tno.nl/saref).