This key has been produced in collaboration between the Universitites of Trieste (Italy) and Graz (Austria) within the European project KeyToNature, for being tested by schools. It includes the most frequent epiphytic lichens which occur in the urban and suburban areas of Graz (Austria). Macrolichens (foliose and fruticose forms) can be identified without the use of microscopical characters, while for the identification of microlichens the use of a good microscope is often essential.