Wagon numbers are key data for railway operations. They enable a railway wagon or coach to be positively identified and form a common language between railway operators, infrastructure companies and the state authorities. The system of wagon numbering has been laid down by the International Union of Railways and is similar to that used for the locomotives and multiple units. Vehicle numbering is now governed by the Intergovernmental Organisation for International Carriage by Rail and in Technical Specifications for Interoperability (TSI) of the European Union.