Fine or ultrafine particulate matter (PM) is a mixture of solid and liquid particles, including carbon?centered combustion particles, secondary inorganics, and crustal?derived particles. Recently, ambient particulate matter has been regarded as a serious health problem in the Republic of Korea. This review focuses on the importance of PM?induced effects, and the adverse health effects from experimental and epidemiological studies. There is widespread evidence that short?term increases in particulate matter result in increased mortality and morbidity in adults and children, even at low levels. Considerable consistency between results from experimental and epidemiological studies has been observed for many health effects, including pulmonary diseases and cardiovascular diseases, although the biologic mechanisms of the health effects are unclear. The adverse health effects are reported to be more pronounced in susceptible population groups such as the elderly, children, or people with preexisting cardiovascular and respiratory conditions. In addition to short?term exposures, long?term exposure to particulate matter is also associated with an increase in total mortality, cardiopulmonary mortality, and respiratory morbidity. The present review suggests that despite a considerable amount of research over the last decades, both epidemiological and experimental studies are needed to further clarify the issues on the effects of fine and ultrafine particulate matter.