Hydrogen cyanide (HCN) is one of the most common astromolecules, found in almost every astrophysical environment. It was discovered by Snyder and Buhl, in the early years of searching for molecules with radio telescopes. The initial observation included detections in 6 sources, W3(OH), Orion A, Sgr A, W49, W51, and DR 21(OH) (which includes an O-type star, protostars, and an H II region). Both the ¹²C and ¹³C isotopomers were observed. Many other interstellar and circumstellar observations of HCN have followed, including the first extragalactic detection in M82 (the Cigar galaxy) by Rickard et al. in 1976. A number of isotopomers of HCN have been found in both galactic and extragalactic sources.

HCN has also been detected in a number of comets, beginning with comet Kohoutek in 1973 by Huebner et al. It's also been observed in comets IRAS-Araki-Alcock, Halley, Hayakutake, and others.

Among solar system planets and their satellites, HCN has been found in Jupiter, Neptune, and Titan.

The cyanide ion (CN^-), which forms when H⁺ is removed from HCN, was recently observed in space for the first time. Another related species, protonated hydrogen cyanide (HCNH⁺), was reported in 1986 by Ziurys and Turner.

Hydrogen cyanide is a well-known terrestrial species as well. It is very poisonous. HCN is close kin to potassium cyanide (KCN), a familiar agent of death in murder mysteries, sometimes assuming the title role as in the case of Agatha Christie's, Sparkling Cyanide. The presence of cyanide is often detected by the "smell of bitter almonds".