First we classify the various emission standards applying to light vehicles, the conditions under which the emissions are measured and the environmental standards. We then describe the way in which a standard is established according to the basic principles and procedures involved in determining acceptable environmental concentrations in practice. We refer to the economic and political considerations involved in deciding on a standard and, as an example, to the positions adopted by the various parties concerned in France when drafting the 15.05 standard. In response to the atmospheric pollution caused by motor vehicles, all the industrial countries have, some earlier than others, drawn up regulations designed to limit the extent of this pollution, to protect the environment and reduce the public health risk. Both environmental and emission standards are aimed at reducing the risks to the environment and in particular to man, arising from the presence of particular pollutants. The procedure concerned in establishing these standards is a complicated one involving scientific, economic and political considerations; furthermore, there is a great diversity of standards.