This Guide describes the causes of corrosion of underground pipelines and the methods of retarding the rate of corrosion to a very low value. The cost of effective corrosion control is about 1-2per thousand of the total cost of laying a pipeline, and is recovered many times over by the consequent extension of the life of the pipe. The Guide is concerned with metal pipes made of iron or steel. Pipes made of other metals (copper, aluminium and stainless steel) are little used and are not considered here, although they deteriorate for much the same reasons.