In recent years, major progress has been made as regards the knowledge and understanding which has been gained of the impact of air pollution. In this study, the basic concepts are set out regarding this subject, and the different possible approaches as far as methodologies are concerned are reviewed. Among the epidemiological studies, the time series studies are those most often used for assessing the short-term impact of air pollution. The most important factors leading to confusion in this type of study are the seasonal and weekly changes, the tendency, the weather variables and the serious illnesses of a seasonal pattern, such as the flu. The main short-term impact of air pollution on human health range from a rise in the overall death rate resulting from respiratory and cardiovascular diseases to the worsening of lung function and other symptoms, including a rise in the number of doctor visits and hospital admissions. Despite a widespread consensus existing with regard to the harmful impact of air pollution, there are a number of questions currently in the need of further research.