The word biomarkers can have many meanings, but in the present context it refers to measurable properties which indicate that a subject has a particular susceptibility, has had a particular exposure, or is demonstrating a particular response to some known or unknown external perturbation. Taken together, these properties of biomarkers offer an approach to monitoring individuals in an environmental or occupational setting, and thereby estimating future, current, or integrated risk. The development and application of such methods promises the possibility of protecting workers, documenting their individual exposure histories, identifying threatening work situations, ameliorating potential adverse effects, and ultimately assigning responsibility for any risk that may have accumulated.