The eXtensible Markup Language (XML) has recently become the W3C Standard for commu nicating data over the Internet. The e- commerce industry and several new software applications have embraced this technology taking advantage of the potential for re-usable and interoperable data. In order to take advantage of XML, each industry is coming up with standard tag terminologies such that the data can be self describing and understandable, independent of the application creating or using it. Adopting XML for energy simulation data representation would enable different simulation programs to work with a single data format and allow other applications to make use of this data or even produce part of this data. EnerXML schema is a proposal to standardize tag terminologies for energy simulation data such that applications interested in interoperability can provide an Application Program Interface (API) conforming to this schema. This paper presents an overview of interoperability issues, introduces the XML concept and describes the proposed framework for EnerXML chema.