  Polycyclic aromatic hydrocarbon (PAH) molecules, ubiquitously seen in the
interstellar medium (ISM) of our own and external galaxies, might have been
incorporated into comets if they are formed from relatively unprocessed
interstellar matter. The detection of PAHs in comets would be an important link
between the ISM and comets. This review compiles our current knowledge on
cometary PAHs, based on ground-based and space-borne observations of infrared
vibrational and ultraviolet fluorescence spectra of comets, and laboratory
analysis of interplanetary dust particles possibly of cometary origin and
cometary samples returned to Earth by the Stardust spacecraft. The latter
provided the most unambiguous evidence for the presence of PAHs in cometary
nuclei.
