Interoperability has become a keyword in the European Transport Policy, with the strong objective to improve transportation services. In the rail sector, this trend is embodied in technological innovations: A deep change in the communication and signalling system is taking place with the new ERTMS projects (European Rail Traffic Management System). This new technology will constitute in the future an important improvement of performances of the rail transportation system, in term of interoperability between railways networks, in term of capacity and in term of traffic management. Such a systemic innovation is however a big challenge: It impacts equipment of infrastructures, rolling-stock, control centres as well as operating rules. Introducing such changes on a complex rail network with high traffic density is not an easy task: How implementing disruptive technologies in an incremental manner? After a short presentation of ERTMS and its expected benefits, this paper examines the stakes of such an innovation through a case study approach, based on the recent experience of SBB and of the Industry (Swiss experience and international overview).