Mercury is toxic to humans; its effects depend on its chemical form, the route of exposure, the timing and duration of exposure, and the dose absorbed. Mercury is not only harmful to the health of vulnerable populations (fetuses, children, pregnant women) but is also toxic to adults. The main effects associated with oral exposure to organic mercury compounds are neurological in nature, including developmental neurotoxicity. Symptoms of mercury-related hydrargia include tingling sensations, vision, hearing, taste, and smell disorders, speech difficulties, muscle weakness and irritability, memory loss, and sleep disturbances. Since the central nervous system is the primary target organ for organic mercury, exposure of the fetus or young child to organic mercury can affect nervous system development, motor skills, attention, verbal learning, and memory. Methylmercury, the most toxic form of mercury, has been classified by the IARC (International Agency for Research on Cancer) as a possible human carcinogen (Group 2B), particularly for kidney cancer. The United Nations Environment Programme’s (UNEP) assessment of mercury concluded that there is sufficient evidence of mercury’s harmful effects to justify international action to reduce risks to human health and the environment. The Minamata Convention, a legally binding global agreement, aims to reduce atmospheric emissions, the supply, trade, and use of mercury worldwide and to find solutions for the environmentally sound management of mercury and mercury waste. In France, the National Nutrition and Health Survey (ENNS) estimated levels of mercury exposure in hair among the general population—including both children and adults—in 2006–2007 [1]. Additionally, in 2011, the perinatal component of the national biomonitoring program (Elfe) provided data on hair mercury levels among pregnant women in France [2]. However, no French study to date had measured urinary mercury in the general population, with the exception of the Imepoge study in 2008–2010 among the adult population in northern France [3]. The results obtained through the Esteban cross-sectional study (Health Study on the Environment, Biomonitoring, Physical Activity, and Nutrition) thus make it possible for the first time to measure urinary mercury in the general population in France and to provide a new estimate of hair mercury exposure levels in the mainland French population aged 6 to 74 years between April 2014 and March 2016. Regarding hair mercury, the detection rates were 100% among children and 99.6% among adults. The geometric means were 0.31 µg/g of hair among children and 0.59 µg/g of hair among adults, respectively. The levels of mercury exposure via hair observed in the Esteban study are very comparable to those observed in ENNS 10 years earlier. The investigation of exposure determinants confirmed dietary exposure factors known in the literature, such as the consumption of fish, crustaceans, shellfish, and mollusks, as well as lifestyle-related factors such as hair treatment. For urinary mercury, the detection rates were 99.4% in children and 95.6% in adults. The geometric means were 0.90 µg L⁻¹ (0.89 µg g⁻¹ of creatinine) in children and 0.75 µg L⁻¹ (1.00 µg g⁻¹ of creatinine) in adults, respectively. The exposure factors identified were the presence of gray dental amalgams, consistent with the literature, in both children and adults, and to a lesser extent, the consumption of fatty fish, crustaceans, shellfish, and mollusks. The levels of urinary mercury exposure in the French population observed in this study are higher than those observed in certain European countries and in North American countries. Esteban’s results enable ENNS to monitor changes over time in the population’s mercury exposure via hair samples, provide the first data on urinary mercury exposure, and update the list of factors influencing mercury exposure. The exposure reference values (ERVs) established as part of this study could help support government public health strategies.