This article reviews the research on the relation between indoor air pollution exposure and acute respiratory infection (ARI) in children in developing countries. ARI is a cause of death globally, causing approximately 19% of all deaths before the age of 5 years, according to a World Health Organization estimate. Indoor air pollution from biomass fuels, which is strongly poverty related, has long been regarded as an important risk factor for ARI morbidity and mortality. The empirical base for this view is comparatively narrow, with few empirical studies in relation to the magnitude of the global public health importance of the problem. Most existing reports consistently indicate that indoor air pollution is indeed a risk factor for ARI, but studies are generally small and use indirect indicators of pollution, such as use of biomass fuel or type of stove. Exposure assessment for indoor air pollution in developing countries is recognized as a major obstacle because of high cost and infrastructural limitations to chemical pollution sampling. Use of proxy indicators without measurement support may increase the risk of both misclassification of exposure and of confounding by other poverty-related factors. The issue of sufficient sample size further underlines the need for decisions to invest in this research field. Areas where further research is needed also include exploring qualitatively options for interventions that are culturally and economically acceptable to local communities.