Growing awareness of the disadvantages of uncontrolled corrosion has, in recent years, led to the development of increasingly sophisticated and costly methods of coating metals used in construction and engineering. It is now possible to specify and provide coatings on metal that will afford almost any required degree of control of the corrosive effects of almost any environment. Furthermore, it is possible to predict, with reasonable accuracy, how long such a coating will perform its control function in its working environment before it requires renewal or renovation. However, a coating cannot fulfil expectations unless it starts its tour of duty in perfect condition. The difficulties of ensuring this are enumerated in this Guide.