Mercury in the environment originates from both natural and anthropogenic sources. The latter, especially released from the use of fossil fuels, substantially surpasses the natural emissions. Mercury uses have resulted in occupational exposures in several occupations and nonoccupational exposure occurs mainly through the consumption of fish, a result of bioaccumulation and biomagnification of methylmercury. Adverse health effects depend on the degree of exposure and the kind of mercury in question, but children and the fetus are notably more susceptible, especially to methylmercury toxicity. Although exposure limits have been lowered, and some uses are being phased out, much remains to be done with respect to limiting human mercury exposure.