Depending on whom you ask, PAHs are either the smallest dust particles or the largestgas-phase molecules in space. Whether referred to as gas or dust, these PAHs can containup to20% of the total cosmic carbon abundance and as such also play an important role inthe carbon chemistry of protoplanetary disks. The interpretation of PAH bands is often acomplex procedure involving not only gas physics to determine their ionization stage andtemperature, but also radiative transfer effects that can bury these bands in a strongthermal continuum from a population of larger dust particles.

PAHs are most readily seen in the spectral energy distributions (SEDs) of disks aroundHerbig AeBe stars where they are photoprocessed by the stellar radiation field. Resolvedimages taken in the PAH bands confirm their origin in the flaring surfaces ofcircumstellar disks: if the SED is consistent with a flat disk structure (lessilluminated), there is little or no evidence of PAH emission. The very low detection ratesin the disks around T Tauri stars often require an overall lower abundance of PAHs inthese disk surface as compared to that in molecular clouds.

In this review, I will adress three aspects of PAHs in protoplanetary disks: (1) Do PAHsform in protoplanetary disks or do they originate from the precursor molecular cloud? (2)Is the presence of PAH features in SEDs a consequence of the disk structure or do PAHs infact shape the disk structure? (3) How can we use PAHs as tracers of processes inprotoplanetary disks?