Surface coatings are considered to be the best protective method against gas side corrosion, friction, and wear. As the basic requirements for coatings, i.e., good adhesion, chemical stability, and high structural and phase stability, and the most important coating methods, i.e., electrolysis and thermal methods, such as pack cementation, plasma spraying, and detonation gun, and chemical and physical vapor deposition are independent of the aim of protection, it is possible to deal with them together. The main program can be divided into four parts: coating development, screening, long-term testing, and studies of behavior on full-size or nearly full-size components. The development phase, the experience gained during the screening period, the change from simplex to duplex, triplex, and graded coatings, and the choice of candidates for the long-term testing program are examined.