After a brief introduction to air quality standards in the European Union (EU), the need for standards is discussed, concluding that they provide an impetus for governments and local authorities to act to reduce pollution and a means for the public to check on the progress of actions by governments, and that in a large region like the EU, they provide a form of environmental equity of a common standard of air quality throughout the region. Discussion follows on the distinction between legal standards which are binding on governments and air quality guidelines which are set with no regard for feasibility of attainment. Impacts on public health are discussed, including the relationship between standards and thresholds of no effect. The statistical nature of standards is discussed, as is the relationship between regulating air quality through the use of standards compared with the use of an exposure-response relationship for a given pollutant. Finally, recent developments in air quality legislation, embodied in the 2008 Air Quality Directive, are described, where it was recognised that relying purely on air quality standards - the achievement of which may not guarantee the absence of adverse effects - may not be the most effective way of improving public health. The 2008 Directive therefore incorporated the concept of 'exposure reduction' where, alongside binding limit values or 'standards', EU Member States are obliged to make progressive reductions of PM2.5 across entire urban areas, regardless of whether or not the conventional 'standards' are met.