Introduction: Radon is a naturally occurring radioactive gas classified as a known lung carcinogen in humans. In France, radon is the leading source of exposure to ionizing radiation, even ahead of medical exposures. The objectives of this study are to describe radon levels in homes and to examine the factors influencing indoor radon levels, based on a representative sample of French homes. This work complements that carried out by the Institute for Radiation Protection and Nuclear Safety (IRSN) in 2011–2013 based on radon measurement campaigns in homes and the mapping of geogenic radon potential. Materials and methods: Housing characteristics and concentrations of indoor pollutants, including radon, were collected between 2003 and 2005 during the national "Housing" campaign conducted by the Observatory of Indoor Air Quality (OQAI), using a representative sample of primary residences in mainland France. A generalized linear regression model was used to determine the factors influencing the radon levels measured inside homes. The analysis was conducted taking into account the sampling plan and the seasonal factor. Results: the arithmetic mean of indoor radon concentration was 61 Bq/m³ [95% CI: 50; 71] and the geometric mean was 37 Bq/m³ [95% CI: 33; 41]. The factors significantly associated with indoor radon concentration were the geological nature of the soil, the presence of a heating or air conditioning system, the floor level, the presence of a chimney, and the building material of the dwelling. The regression model explained 40% of the variability in the observed radon levels. A significant correlation was observed between indoor radon concentration and indoor gamma radiation dose rate (r=0.22). Conclusion: This study provided a better characterization of the determinants of radon concentration inside homes in France. The determinants identified in this study are consistent with those found in other recently published studies. (R.A.)