Modern railway operation today requires direct, rapid and permanent contacts between the different levels of management. It is therefore essential for these different levels to be properly and instantly informed so that they can take rapid action on any matter coming within their scope and issue the necessary instructions. Such organisation is valid only if it has proper telecommunications facilities, the characteristics of which may differ depending on the service demanded of them. Introducing such facilities generally calls for large-scale capital investment. The purpose of this leaflet is to assemble information on the experience acquired by the different Railway Undertakings (RUs) in connection with the rationalisation of operations and development of methods made possible by the ever increasing use of telecommunications. Other leaflets, numbered in sequence, deal with the purely technical aspects of the different telecommunications systems that may be used. The procedures for improving the operating methods of a railway differ according to its size, the density of its traffic and, above all, to the organisation of its management structures. Depending on whether this organisation is wholly centralised (single headquarters) or fully decentralised (regional headquarters with large-scale autonomy) or else partly centralised (central headquarters with departments directly involved in the performance of certain operating tasks, and regional headquarters or divisions with limited autonomy), the telecommunications facilities required are organised in different ways.