The design and operation of machine telegraph systems has been very considerably affected in recent years by the production of high-speed communication links of the transoceanic order of length, and by new methods of operation on land lines enabling the line plant unit—the telephone pair—with its series loading and its repeater stationsen routeto be used for either the transmission of telegraph signals or speech, or both, simultaneously and independently.The regenerative repeater, by enabling several sections of cable and land line to be interlinked, has given rise to methods of operation far reaching in their effect both from the point of view of economy to the Administration and from that of reliability and speed to the user.While the possibility of connecting two remotely situated medium-traffic offices over a single channel of a main-line high-speed multiplex system has been known for a number of years, this has not led to any considerable developments in that direction. Conditions are, however, arising in which medium traffic offices will use start-stop single-channel systems to an increasing extent, and this is being influenced by the large number of channels rendered available by the dual use of the land telephone cable. Wherever the telephone network extends, the telegraph network is ready to hand, and the single-channel system will, in course of time, replace the multiplex system for inland telegraphy.The long-distance links with their regenerative repeaters require a precision in speed and phase control not necessary heretofore, and a study of this subject therefore forms a considerable portion of this paper.The sending and receiving apparatus of the start-stop single-channel system are the inverse of each other, and the paper endeavours to establish a general underlying principle for the different variants described.The last phase of machine telegraphy will certainly be that in which intercommunication between centres will be automatically effected and intermediate manual transmission avoided. This is possible by reason of the large number of channels available through the previously-mentioned dual use of the wire plant, and by the present-day standard of automatic switching technique.