Agricultural crop production is highly dependent upon environmental conditions among which air quality plays a central role. Various air pollutants have been identified as a potential influence on commercial crops including SO 2 , NOx, O 3 and CO 2 . In particular, ozone in the lower atmosphere has been identified as a serious cause of crop loss in the United States and seems likely to be creating similar losses in Europe. In this paper the methods which can be applied to assess the economic damages from air pollution are critically reviewed. This requires measuring pollutant concentrations, relating these to physical crop damages, and estimating the reactions of the agricultural sector and consumers to give welfare changes in terms of consumers' surplus and producers' quasi-rents. The approach of the European open-top chamber programme (EOTCP) is shown to have neglected lessons learnt by the National Crop Loss Assessment Network (NCLAN) in the US