In recent years there have been considerable reductions in the amount of NOx emitted by burners fired by natural gas, oil or pulverised coal. This has been brought about by a number of approaches such as reducing the temperature and by fuel staging, both of which minimise the NOx-forming reactions in fuel-rich zones, In gaseous or light-fuel flames this reduction in NOx is considerable-80-90%-but in the combustion of pulverised coal it is only about 50-60%. Thus there is considerable interest in reducing NOx further, and this is the subject of a number of collaborative research projects such as the current UK DTI-NOx project. In this review the NOx-forming reactions are discussed, giving an indication of the way that they can be used for computational fluid dynamic (CFD) modelling of flames. A number of applications are considered, including natural-gas burners and staged oil-spray flames, where in both cases prompt-NOx becomes dominant at low NOx levels. However, particular attention is devoted to combustion of pulverised coal and some of the DTI-NOx project results from laboratory experiments. An ＇advanced coal model＇ detailing some aspects of the work is outlined; in this, details of devolatilisation of speciated volatiles, including HCN, are also included for a number of coals. The char left by the devolatilisation process is a porous carbonaceous material, and a model is given for the formation of network char and cenospheres, and the subsequent reaction of the fuel-nitrogen compounds in the char to give NOx. The effect of coal composition, rank, and the nature of the nitrogen functionalities on NOx formation, and on residual carbon burn-out, are discussed. Methods of improving NOx are considered.