Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Wagon numbers (or coach numbers) are key data for railway operations. The wagon number enables a railway wagon or coach to be positively identified and forms a common language between railway operators, infrastructure companies and the responsible state authorities. The system of wagon numbering described below has been laid down by the International Union of Railways (Union internationale des chemins de fer or UIC) and is used in a similar way to that used for the locomotives and multiple units. The complete wagon number comprises 12 digits.