Polycyclic aromatic hydrocarbons (PAHs) as a group have been identified through their aromatic infrared emission bands (AIBs) in many astrophysical objects and environments, including H II regions, reflection nebulae, young stellar objects, planetary and protoplanetary nebulae, post-AGB objects, galactic nuclei and ultraluminous infrared galaxies. In this talk I will describe how spectroscopic and spatial observations of objects including the Red Rectangle and NGC 7023, coupled with spectral modelling, enable us to investigate the formation and evolution of PAHs and their role as probes of astrophysical conditions and processes.