In Memory of Klaus Hafner

This Guest Editorial and Special Issue of European Journal of Organic Chemistry are dedicated to the memory of Klaus Hafner (1927-2021), who played an import role to establish this journal and who served as Senior Editor of the predecessor journal Liebigs Annalen der Chemie. As one of the outstanding chemists of the second half of the 20th century, he was a pioneer of the chemistry of nonbenzoid pi-systems and their metal complexes.