This new issue of Extrapol presents epidemiological studies that have sought to assess the health impacts of measures aimed at reducing air pollution levels. This type of research is of primary interest to policymakers and public agencies, such as the French Environment and Energy Management Agency (ADEME), which are responsible for monitoring air quality and implementing or promoting policies aimed at reducing air pollution. These studies measuring the health effectiveness of interventions are first and foremost of interest from an epidemiological perspective, particularly regarding urban air pollution. Experimental evidence, in fact, ranks among the commonly used criteria for causality proposed by Hill. However, this “evidence” is, of course, difficult to gather since we rarely find ourselves in a controlled situation involving a clear reduction in exposure. We must therefore be grateful to these epidemiologists for having seized the opportunity presented by sudden changes in emissions to assess their health benefits. This further strengthens confidence in the causal nature of the relationship between urban air pollution and health, and thus the legitimacy of health impact assessments of urban air pollution. (Excerpt from the article)