What is the telecommunications industry? How does it relate to other activities in areas such as computing, software, semiconductors, the internet and electronic commerce, and the media? Where are its boundaries? What products and services should be included within it? What are its major markets? Which companies should be included in the industry? In this paper, we tackle these important questions by developing a layer model in order to map the industry. Layer models generally have a long and distinguished history in the telecommunications and computing fields. In the area of engineering and software design, they allow engineers to reduce and render tractable the awesome complexity of complex systems. They help to achieve this purpose essentially by decomposing the system into relatively autonomous subsystems that interact with each other through an interface that is often standardized in order to facilitate coordination. But, in this paper, the layer model does more than merely decompose a complex system into component subsystems. While each layer may be thought of as a subsystem (usually further subdivided into sub-sub-systems, and even further subdivided), the layer model also, by its nature, draws attention to the interdependence of each layer on the layers below and above it. By decomposing the telecommunications industry into different layers, and further by analysing the interdependence between the major layers that compose the industry, we will provide a detailed assessment of an industry, characterized by recurrent technological innovation and faced with an increasing diversification of demand. The reader should note that this article draws heavily on our telecoms website: http://www.TelecomVisions.com.