Computer and data networks are the mechanism by which information systems are interconnected. The underlying techology and the principles of design for the architectures of such networks are still limited but the demands placed upon them are of continually increasing sophistication. The paper reviews the ways in which a classification of networks can be determined, thereby providing a perspective for the designers of modern communication networks. It is the classification of networks (based upon wide-area networks, metropolitanarea networks and local-area networks) which causes great confusion and so the paper sets out to explain how the ‘spirit’ of classification should be used and not necessarily the ‘law’ in order to appreciate the characteristics of the various types of network.