Engineers have been dealing with deterioration in concrete structures since shortly after their initial use. Before 1980 deterioration was taken into consideration predominantly using rules of thumb developed through experience. After 1980 simple engineering models, such as Fick's law, the Hetek's model and time dependent models, were developed and became more widely used. With time these models, both deterministic and stochastic, are becoming increasingly more sophisticated and are increasingly based on "physical" parameters. This trend will continue and future models will be based even more so on the physical, chemical and mechanical laws and principles that govern material and structural behaviour.