Coatings applied by halide activated pack cementation will be discussed. Specific examples including aluminizing and chromizing of substrates such as nickel and stainless steels will be presented. The evolution of coating microstructures as a function of coating process parameters e.g. temperature time activator salt and pack composition will be discussed. Coating mechanisms will be proposed and discussed with reference to the literature. Exposure test data will be reported as available. The potential of these coatings for chemical process applications will be outlined.Key Words: Coatings pack cementation aluminizing chromizing