Because cinnabar is the only important ore of mercury, the demand for mercury has driven mining activity. Mercury has many uses, but its toxicity has reduced its use in any application where reasonable substitutes can be found. Large amounts of mercury are currently used in the chemical industry in the production of chlorine and caustic soda during the electrolysis of brine.

Mercury was widely used in temperature- and pressure-measuring instruments such as thermometers and barometers. It was often used in gravity switches because it flowed easily as a liquid and conducted electricity. Most of these uses have been discontinued.

Mercury is currently used in some batteries and light bulbs, but their disposal is often regulated. Because it is toxic, it was once widely used to protect seed corn from fungus and to deworm materials used to make felt. It was used in dental amalgam but is being replaced by polymer resins and other materials. In almost all of its use, mercury is being replaced with less toxic and nontoxic substitutes.

Mercury has been widely used in mining to separate gold and silver from ores and stream sediments. Large amounts of mercury were spilled during these operations, and today, mercury used in the 1800s is still being recovered from streams.