This report describes the results of two projects undertaken to study the long-term carbonation of reinforced concrete. The first was a joint project between the British Cement Association (BCA) and the Building Research Establishment (BRE) to examine the influence of materials and workmanship factors and types of elements on the rates of carbonation under site exposure conditions. The second was initiated by BRE to assess (under the DOE research programme) the effects of practical site curing methods on the long-term carbonation rates of concrete made with different cements.