SRON/Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
The near-infrared emission spectrum of the interstellar medium is
dominated by IR emission features at 3.3, 6.2, 7.7, 8.6, and 11.3 
.
These features are commonly ascribed to Polycyclic Aromatic Hydrocarbon
(PAHs) molecules containing 20-100 C atoms. The SWS on ISO has provided
us with spectra from 2.5-45
of a large variety of sources
associated
with bright FUV sources such as HII regions and reflection nebulae.
These observations reveal the incredible richness of the near-IR
spectrum. Apart from the features mentioned above, there is a wealth of
weaker features present as well. These studies also reveal detailed
variations from source to source which may be of key importance in the
detailed molecular identification process. ISOPHOT and ISOCAM have
shown that these features dominate the near-IR cirrus emission in the
Milky Way as well as the emission from the ISM in other galaxies and
hence, besides dense photodissociation regions, these species are
also ubiquitous in the diffuse ISM. These observations will be
reviewed. Important questions still remaining will be pointed out.