Mercury, also called quicksilver, is a chemical element in the periodic table that has the symbol Hg (Latinized Greek: hydrargyrum, meaning watery or liquid silver) and atomic number 80. A heavy, silvery transition metal, mercury is one of five elements that are liquid at or near room temperature and pressure. (The others are the metals caesium, francium, and gallium, and the non-metal bromine.)

Mercury is used in thermometers, barometers and other scientific apparatus, though concerns about the element's toxicity have led to mercury thermometers being largely phased out in clinical environments in favour of alcohol-filled, digital or thermistor-based instruments. It remains in use in a number of other ways in scientific and scientific research applications, and in dental amalgam. Mercury is mostly obtained by reduction from the mineral, cinnabar.

Mercury occurs in deposits throughout the world and it is relatively harmless in an insoluble form, such as mercuric sulfide, but it is poisonous in soluble forms such as mercuric chloride or methylmercury.