A brief history is given of the classification by the Building Research Establishment of sulphate-bearing ground, and of concrete resistance to sulphate attack. The original classification in 1939, based on sulphate in groundwater, consisted of three limits based upon the testing of different concretes in sulphate solutions of different compositions and concentrations. Further classes of greater severity were added in 1968. The limits were adjusted in 1991 to convert from measurements of SO3 to SO4, and the limit for magnesium ion concentration of 1g/litre was introduced. A classification based on the sulphate in water/soil extracts was introduced in 1968, which gave greater emphasis to the more soluble magnesium and sodium sulphates. By the 1990s, the potential contribution from pyrite was recognised, and a test procedure added to the British Standards. 15 refs.