Interoperability between fare systems is an important step towards “seamless travel” and is a necessary condition for the efficient provision of passenger information on fares across transport modes. Achieving this goal presents a technical challenge and to help reach it the European project NeTEx/EPTIS proposes a standardised data exchange format for fares that can be used across Europe. The project specifies how to model the complexity of European fare structures, using a data model based on generic concepts that can represent the core elements of any fare system, independently of any specific set of concrete fare products offered for sale, and then derives a standard interface as an XML schema implementation. The European Reference Data Model for Public Transport (Transmodel), extended to cover the requirements of heavy rail, is used as a basis for the proposed fare model. An early implementation of NeTEx is achieved by the project BIPEx.