In 1861, rubidium was discovered spectroscopically when a very distinctive, ruby-red colour spectral line was observed. The new element was given the name rubidium, from the Latin name rubidus, meaning "deep red".

Rubidium is an alkali metal. It is one of the few metals that can exist in its liquid form in a slightly warm environment (melting point is 39^oC). As a member of this group, it is highly reactive and cannot exist in its elemental state in nature because it reacts with air and moisture to produce compounds. Rubidium undergoes spontaneous combustion when exposed to air at room temperature. It also reacts violently in water. The pure metal has to be stored and transported in containers of kerosene or nitrogen gas, or in a vacuum bottle.

Rubidium can be found as an impurity in lithum and cesium ores. Most rubidium is recovered from the byproducts of lithium-refining operations. Naturally occurring rubidium comprises of two isotopes, one of which is radioactive.

Rubidium's chief uses are in electronic devices such as vacuum tubes, cathode-ray tubes, and photocells. It has been used to locate brain tumours, as it collects in tumours but not in normal tissue.