Among the tools available for assessing the exposure of workers and the general population to chemical substances, biological exposure monitoring occupies an important place alongside atmospheric pollutant metrology. This approach offers a number of advantages (multisource, multiscale exposure, integration of protective equipment, consideration of individual factors) and is the tool of choice for monitoring exposure to substances with chronic systemic toxicity (carcinogenic, neurotoxic, nephrotoxic, bioaccumulative). Its implementation, based on the measurement of exposure biomarker concentrations (more rarely effect biomarkers) and their comparison with interpretive biological values, makes it possible to verify risk control and, if necessary, adapt the medical monitoring of subjects. This typically multidisciplinary approach, involving both the occupational health physician and the prevention team (nurses, occupational risk prevention specialists, toxicologists), calls for a systematic and rigorous methodology, as well as the protocolization of several stages to save time and harmonize practices. Last but not least, it helps to ensure the individual and collective trac¸ability of exposures, which is essential for post-professional monitoring of employees, possible compensation, epidemiological studies and public occupational health policies.