In organic chemistry, a ketene is an organic compound of the form , where R and R' are two arbitrary monovalent chemical groups (or two separate substitution sites in the same molecule). The name may also refer to the specific compound ethenone , the simplest ketene.
Although they are highly useful, most ketenes are unstable.  When used as reagents in a chemical procedure, they are typically generated when needed, and consumed as soon as (or while) they are produced.