Lithium, a soft alkali metal with a silver-white colour, is the lightest metal and the least dense solid element.  Appearing in the periodic table as the first element in Group I, the alkali metals group, like the other metals in the group - sodium, potassium, rubidium and cesium - it is so chemically active that, in nature, it never occurs as a pure element, but is always bound in stable minerals or salts.  It corrodes quickly in moist air to form a black tarnish.  Due to this high reactivity it only appears naturally on Earth in the form of compounds.  Reactions of lithium metal with water, oxygen, carbon dioxide and a host of other elements - even nitrogen - are possible at room temperatures. Yet many lithium compounds, especially those formulated for the ceramics industries, are as inert as common sand. This seemingly paradoxical behaviour makes lithium extremely useful.

Lithium occurs in a number of pegmatitic minerals, but is also found in some brines and clays.  Trace amounts of lithium are present in the oceans and in some organisms, though the element serves no apparent biological function in humans. Nevertheless, the neurological effect of the lithium ion Li+ makes some lithium salts useful as a class of mood stabilizing drugs. Lithium and its compounds have several other commercial applications, including heat-resistant glass and ceramics, high strength-to-weight alloys used in aircraft manufacture, and in lithium-based batteries.  Lithium also has important links to nuclear physics: the splitting of lithium atoms was the first man-made form of a nuclear reaction, and lithium deuteride serves as the fusion fuel in staged thermonuclear weapons.  However, the fastest growth in the demand for lithium over the next few years is expected to be from lithium battery production, especially for electric and hybrid-electric vehicles.

Current global resources and reserves have been estimated at 28 million tonnes of lithium, equivalent to more than 150 million tonnes of lithium carbonate, of which nearly 14 million tonnes of lithium (74 million tonnes of lithium carbonate) are found at active or proposed operations. Currently, the Salar de Uyuni in Bolivia is the largest known lithium deposit, with resources of approximately 5.4 million tonnes of lithium metal, but is not being exploited due to political considerations.