A number of by-products, such as ash, slag, dust and toxie gases are produced during exothermal reaction of coal burning. The gases emitted into the constitute the very serious problem due to considerable difficulties related to gases removal. This applies chiefly to sulfur and nitrogen oxides. In 1998, the Ministry of Environmental Protection, Natural Resources and Forestry issued the ordinance regarding the permissible level of pollutants emitted into the atmosphere as a result of hard coal burning. The ordinance was aimed at adjusting the Polish standards to European Union standards. Also the European Union countries modified their regulations and in the year of 2001 approved two Directives regarding the emission of sulfur dioxide and nitrogen dioxide. The paper deals only with the nitrogen oxides problem. The genesis of their origin, the emission standards and the emission level have been presented. The mechanisms of converting the nitrogen into the nitrogen oxide and nitrogen dioxide have been discussed, as well as the impact of temperature on NOx generation has been explained. In the light of awareness with regard to the reasons for and effects of the nitrogen oxides, the efficient methods of counteraction have been presented. These include the primary methods involving the prevention of oxides generation, and secondary methods, restricting the emission of oxides already generated. The problem of nitrogen oxides is very complicated and requires further research and enhancing of the currently used reduction methods.