This Technical Specification provides an Interoperability Model, which will enable an eService compliant with technical requirements, to interoperate with different implementations of the European Citizen Card. This Interoperability model will be developed as follows: - starting from the ECC Part 2, Part 3 of the ECC series provides additional technical specifications for a middleware architecture based on ISO/IEC 24727 (all parts); this middleware will provide an API to an eService as per ISO/IEC 24727 3. - a set of additional API provides the middleware stack with means to facilitate ECC services. - a standard mechanism for the validation of the e-ID credential is stored in the ECC and retrieved by the eService. In order to support the ECC services over an ISO/IEC 24727 middelware configuration, this part of the standard specifies the following: - a set of mandatory requests to be supported by the middleware implementation based on ISO/IEC 24727 (all parts). - data set content for interoperability to be personalised in the ECC. - three middleware architecture solutions: one based on a stack of combined ISO/IEC 24727 configurations and the other based on Web Service configuration whereas the third one is relying on a SAL Lite component. - an Application DiscoveryProfile featuring the guidelines for card-applications to fit in ISO/IEC 24727 framework.