  New research is presented, and previous research is reviewed, on the emission
and absorption of interstellar aromatic hydrocarbons. Emission from aromatic
hydrocarbons dominate the mid-infrared emission of many galaxies, including our
own Milky Way galaxy. Only recently have aromatic hydrocarbons been observed in
absorption in the interstellar medium, along lines of sight with high column
densities of interstellar gas and dust. Much work on interstellar aromatics has
been done, with astronomical observations and laboratory and theoretical
astrochemistry. In many cases the predictions of laboratory and theoretical
work are confirmed by astronomical observations, but in other cases clear
discrepancies exist which provide problems to be solved by a combination of
astronomical observations, laboratory studies, and theoretical studies. The
emphasis of this paper will be on current outstanding puzzles concerning
aromatic hydrocarbons which require further laboratory and theoretical
astrochemistry to resolve. This paper will also touch on related topics where
laboratory and theoretical astrochemistry studies are needed to explain
astrophysical observations, such as a possible absorption feature due to
interstellar "diamonds" and the search for fullerenes in space.
