The objective of the Indoor Air Pollution and Health (IAPAH) research project was to, quantify the levels of Indoor Air Pollution (IAP) in Irish and Scottish homes where open combustion takes place, and provide an estimate of the potential health burden due to exposure to combustion derived air pollution in the home. IAP concentrations were measured in 100 homes in Ireland and Scotland. Open combustion was defined as the use of the solid fuels; coal, wood, peat, for heating, gas for cooking or the presence of tobacco smoking. Twenty four hour data on airborne concentrations of particulate matter smaller than 2.5µm (PM2.5), carbon monoxide (CO), carbon dioxide (CO2) and endotoxin, together with 2-3 week averaged concentrations of nitrogen dioxide (NO2) were collected. Concentrations of IAP in homes using coal, wood, peat and gas for cooking were low, and mostly well within health based standards, suggesting adequate ventilation, and well maintained combustion systems in the participating homes. PM2.5 concentrations in homes using coal, wood and gas cooking using homes were comparable to outdoor ambient concentrations. Peat burning homes had PM2.5 concentrations approximately twice that of ambient air, whereas smoker homes had PM2.5 concentrations greater than ten times the level measured in coal, wood and gas cooking homes. The average 24-hour PM2.5 concentrations in smoker homes are the main cause for concern in terms of IAP from combustion sources in the home. The average 24-hour PM2.5 concentrations was almost six times the World Health Organisation (WHO) 24-hour PM2.5 guidance concentration value of 25 µg/m3, and over 4 times the US Environmental Protection Agency (EPA) outdoor Air Quality index ‘unhealthy’ level for sensitive groups of 65 µg/m3 guidance values, and two modified versions of the ‘full chain approach’ to Health Impact Assessment (HIA), the source based approach and the pollutant based approach, were used to estimate the health burden from solid fuel combustion and environmental tobacco smoke (ETS) in the home. The source based approach uses a simple binary exposure metric, which requires information on the proportion of the population exposed to the pollutant source, risk functions for health outcomes associated with the presence of the source, and background rates of disease in the unexposed population for the health endpoints of interest. The pollutant based approach uses a signature pollutant, in this case, PM2.5, as a marker of the pollutant source of interest, and requires information on the exposure to PM2.5, information on the population exposed, exposure response functions linking exposure with mortality and morbidity, and background rates of morbidity and mortality in the exposed population. Within IAPAH the source based approach was used to estimate the burden on health from exposure to ETS within the home. Two populations were considered, non- or never-smoking children (< 15 yr) and non- or never-smoking adults (< 25 yr) who live in a smoking household. The pollutant based approach was used to estimate the health burden attributable to burning solid fuels, using gas cooking and exposure to ETS in the homes. When estimating the health impact attributable to burning solid fuel and using gas cooking in the home two exposure scenarios were considered, exposure to the source from 6 pm until midnight, or for 24-hours. PM2.5 data were adjusted for the contribution of other indoor and outdoor sources. This resulted in the homes using gas cooking being considered as a control group for the other solid fuel homes. Concentrations of PM2.5 in coal and wood homes were low and so health impacts were not calculated. Concentrations of PM2.5 in homes using peat were slightly higher and health impacts were calculated for the exposed population in Ireland only. Results from the health impact assessment indicate that exposure to ETS represents the greatest impact on health from combustion derived air pollution in the home. Both the source based approach and the pollutant based approach estimate cardiovascular events as the greatest health burden among adults and lower respiratory illness and respiratory symptoms among children who are exposed to ETS at home. Health burden estimates, calculated using the pollutant based approach are higher than those calculated using the source based approach. The exposure of non-smokers to ETS in the home accounts for a health burden that is broadly comparable to that currently experienced in both countries from road traffic accidents and there is a real need for public health policy and research professionals to develop interventions to address this. We recommend that co-ordinated national campaigns to educate smokers and non-smokers about the health effects of ETS exposure in the home should be developed together with intervention tools to reduce smoking initiation and increase quitting. Research to identify methods that help those who continue to smoke to implement smoke-free homes is also required. In order to be able to evaluate future progress in reducing non-smokers’ exposure to ETS there is a need to have a question to determine population-wide exposure to ETS at home incorporated in existing national health survey campaigns in both countries.