Abstract: The Levels of Conceptual Interoperability Model (LCIM) has been developed to provide both a metric of the degree of conceptual representation that exists between interoperating systems and also as a guide showing what is necessary to accommodate a targeted degree of conceptual representation between systems. The model was originally developed to support the interoperability of simulation systems, but has been shown to be useful for other domain areas. The model is stratified into seven general levels, and these are introduced and defined. Implied within the model is that the information and processes of one system should be described and that description is then made available to another system. This description of information and processes can take many forms, but is generally an ontological representation. The components of an ontological representation are defined in form and also as elements for the various layers of the LCIM.