  Almost all properties of a photodissociation region (PDR) depend on its
metallicity. The heating and cooling efficiencies that determine the
temperature of the gas and dust, the dust composition, as well as the elemental
abundances that influence the chemical structure of the PDR are just three
examples that demonstrate the importance of metallicity effects in PDRs. PDRs
are often associated with sites of star formation. If we want to understand the
star formation history of our own Galaxy and of distant low-metallicity objects
we need to understanding how metallicity acts on PDR physics and chemistry.
