"Drawing upon a framework of analysis developed by Thomas Hughes, this paper examines the development of the telecommunications network as a large technical system, dealing with the ways in which innovation is behind the rate and direction of system growth. It focuses on developments in the USA and in Europe since the 1960s in a period when a cluster of radical innovations changed the traditional technical and institutional set-up of the telephone network. The paper argues that an explanation of innovation in large technical systems‘has to account for the economic drive to realize economies of scale and scope. However, a new concept of economy of system is required to explain the reductions in cost which stem from innovations that improve the control of traffic, or load, through the telecommunications network and other large technical systems. The argument of the paper is not that economic forces take priority over issues of social and political choice but, rather, that a framework is required which accounts for the ways in which technology and economics mix with politics in the development of telecommunications and other large systems..."