This 1989 book provides an introduction to the immensely important area of computer networking. The book covers everything from systems linked by telephone lines to tightly coupled networks of processors using high speed links, and the correspondingly broad range of techniques that are needed. The emphasis throughout is on the understanding of the principles that may rapidly become out of date. However, detailed discussion of standards and systems is given where they are widely accepted and likely to be long-lasting. In particular the ARPANET and OSI standards are discussed. The author's style is extremely accessible, and many real-life examples are given to illustrate the discussion.