The release of nitrogen oxides during coal combustion has a major environmental impact. In low-NOx burners and fluidized bed combustors the char nitrogen is the major contributor to nitrogen oxide emissions. In this review the release of nitrogen oxides during the combustion of chars is considered in relation to coal and char structural characteristics. The changes in the nitrogen functionality during the conversion of coal nitrogen to char nitrogen are discussed in detail. The results available in the literature relating nitrogen oxide emissions to coal and char properties are discussed in terms of the mechanisms for production of nitrogen oxides and their reduction in the pores or on the surface of the char.