This chapter deals with durability tests intended to characterize the distress caused by the interaction of penetrating deleterious agents with concrete components, leading to deterioration of the concrete itself or of the reinforcing steel embedded in it. Numerous tests have been developed over the years to identify degradation processes and quantify their influence. The most common processes addressed in such tests include sulfate attack, alkali–aggregate reactions and frost attack. Alkali–aggregate tests are intended not only to quantify the risk involved in the aggregates used, but also the influence of the nature of the cement, particularly in view of its alkali content. The resistance to freeze–thaw cycles is dependent on the strength achieved by the concrete and the quality of the air-void system induced into it. The electrical resistivity of the concrete cover is an important parameter controlling the rate of corrosion reactions once depassivation has taken place.