Carbon monoxide (CO), is a colorless, odorless and tasteless gas which moves with air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal biological functions.

It consists of one carbon atom and one oxygen atom, connected by a triple bond which consists of two covalent bonds as well as one dative covalent bond. It is the simplest oxocarbon, and is an anhydride of formic acid.

Carbon monoxide is produced from the partial oxidation of carbon-containing compounds; it forms when there is not enough oxygen to produce carbon dioxide (CO2), such as when operating a stove, furnace, or an internal combustion engine in an enclosed space. In presence of oxygen, carbon monoxide burns with a blue flame, producing carbon dioxide.