Cold fusion is a hypothesized type of nuclear reaction that would occur at, or near, room temperature. It would contrast starkly with the "hot" fusion that is known to take place naturally within stars and artificially in hydrogen bombs and prototype fusion reactors under immense pressure and at temperatures of millions of degrees, and be distinguished from muon-catalyzed fusion. There is currently no accepted theoretical model that would allow cold fusion to occur.

Martin Fleischmann FRS was a British chemist who worked in electrochemistry. Premature announcement of his cold fusion research with Stanley Pons, regarding excess heat in heavy water, caused a media sensation and elicited skepticism and criticism from many in the scientific community.