Josef Hafellner is an Austrian mycologist and lichenologist. He was awarded the Acharius Medal in 2016 for his lifetime contributions to lichenology. Before his retirement, he was a Professor at the Karl-Franzens-Universität in Graz. Hafellner started developing an interest in lichens while he was a student at this institution, studying under Josef Poelt. He earned a master's degree in 1975 and a PhD in 1978, defending a doctoral thesis about the genus Karschia. In 2003, Hafellner received his habilitation. By this time, he had studied with French lichenologist André Bellemère at Saint-Cloud, where he learned techniques of transmission electron microscopy and how their application in studying asci could be used in lichen systematics.
His research interests include the classification and taxonomy of lichens and lichenicolous fungi and lichen floristics of the eastern European Alps. He has made about 100,000 scientific collections of specimens, including about 8000 lichenicolous fungi. Hafellner has introduced more than 600 scientific names to science, and as of 2016, authored or co-authored 289 scientific publications.