Aromatic carbon, in some form, has been an essential ingredient by and large in all
models of the extinction curve, since the original proposal to attribute the bump at 217.5
nm to “astronomical graphite”. This aromatic carbon is most naturally identified, in up to
date models, with a population of Polycyclic Aromatic Hydrocarbons (PAHs), free and/or
clustered. In all models, this PAH population accounts for the far–UV nonlinear rise in
the extinction curve, contributes to the bump and possibly part of the large set of
unidentified, discrete absorption features in the visible (the Diffuse Interstellar
Bands). We review the current state of our understanding of the contribution of PAHs to
interstellar extinction, and what constraints can be imposed on the PAH population by
fitting extinction models to observations.