The diffuse interstellar bands (DIBs) have been known of since 1922, but their carrier
molecules remain unidentified to this day. We present a brief history of DIB observations,
followed by a list of constraints any suggested origin must face, and finally a preview of
current research for ultraviolet DIBs using the Cosmic Origins Spectrograph
on the Hubble Space Telescope. We conclude that PAHs are
consistent with all the listed constraints, but that PAHs may not be the only molecular
species responsible for the DIBs.