Air pollution levels continue to be high worldwide, vary greatly within and between countries, and contribute to a substantial burden of disease. There is convincing evidence that long-term exposure to air pollution adversely affects numerous health outcomes. This chapter presents the recent and growing epidemiological evidence for its effect on respiratory health, focusing on asthma and lung function. Further research should prioritise the pollutant mixtures most detrimental to health and identify the most appropriate health protection measures. Respiratory health is also influenced by outdoor pollen and mould exposures, which are not commonly monitored or regulated by standards. Climate change and interactions with air pollutants influence the growing pattern of outdoor allergens, affecting allergic and asthmatic symptom onset, duration and severity. These changes occur gradually but can result in acute outbreaks of disease, such as thunderstorm-related asthma. While waiting for the implementation of effective controls, there are some limited actions individuals can take to reduce their exposure to air pollution and outdoor allergens.