This chapter examines legal regimes relating to air quality, considering developments at the international, EU, UK and local levels. International and EU law is particularly important in this regulatory sphere since air pollution is a transboundary issue. There is also increasing public concern about air quality, which is reflected in high profile public interest litigation being brought against the UK government to ensure lawful levels of air quality are being met, or at least properly planned for. There are also implementation and coordination problems that make compliance with air quality law a considerable challenge. Regulating air quality ultimately requires coordinating the actions and efforts of actors in many industries, sectors, and geographical areas. At present, not all of those actors are within the scope of UK air quality law.