In chemistry, a cyanide (from Greek kyanos 'dark blue') is a chemical compound that contains a C≡N functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom.

In inorganic cyanides, the cyanide group is present as the cyanide anion ⁻C≡N. This anion is extremely poisonous. Soluble salts such as sodium cyanide (NaCN) and potassium cyanide (KCN) are highly toxic. Hydrocyanic acid, also known as hydrogen cyanide, or HCN, is a highly volatile liquid that is produced on a large scale industrially. It is obtained by acidification of cyanide salts.

Organic cyanides are usually called nitriles. In nitriles, the −C≡N group is linked by a single covalent bond to carbon. For example, in acetonitrile (CH₃−C≡N), the cyanide group is bonded to methyl (−CH₃). Although nitriles generally do not release cyanide ions, the cyanohydrins do and are thus rather toxic.