This presentation will provide information on the backgrounds of interoperable travel documents. Starting with information on the standardisation history and first approaches for guaranteeing interoperability the basic documents are shown which provide the basis for a world-wide interoperability of travel documents. As time passed the request for conformity testing came up, guaranteeing interoperability even when ePassport and ePassport readers are tested and certified separately from each other. Such conformity testing is highly required in a situation where huge amounts of different products are to be expected – such as in the field of travel documents. The ePassports coming from many countries world-wide will be different in make and used components, however, finally the interoperability must be maintained for all of them. Furthermore, the number of ePassport readers (e.g. at border controls) will be under the national control of the various countries. Hence, also here there will be differences between implementations depending on the country in which they are used. As cross-over-testing can only cover a part of the solutions out there with reasonable effort, therefore the conformity testing – combined with a related certification – must be the way of choice to guarantee world-wide interoperability. As an example for a well-functioning certification scheme, the BSI-approach is shown. In the specifications from ICAO the testing is separated into two sections and such is the certification of the BSI as well: Testing of Physical Layer, Timing, Framing, Initialisation, Protocols on one side and Testing of the Applications and Security on the other. These sections are presented completed by the experience made in the accredited test laboratories for ePassport conformity. Afterwards the requirements for the Common Criteria Evaluation and even the Production of ePassports are highlighted. Finally, a short overview is given on the issues, which are still to be addressed in the near future to further improve the already high grade of interoperability. This might open up a new iterative loop on the way to the optimum solution.