This volume focuses on the interaction of lichens with their substrate, environment and their biogeographic effects. In seventeen chapters thirty-eight authors present recent findings and developments in systematics, biodiversity, floristic studies and ecology, as well as newly described taxa, and keys to the identification of Caloplaca and xanthorioid lichens. Molecular phylogenetic analyses of several groups and genera are presented, resulting in an improved systematics of, for example, Caloplaca, Cladonia, Collema and xanthorioid lichens. The genera Arthonia and Usnea in Greece (with key) are reviewed. The volume is dedicated to Prof. Hans Martin Jahns on the occasion of his 70th birthday, featuring papers on some of his favourite fields of research, among them lichen interactions with their substrate and environment and lichen biogeography. A brief biography of Jahns, highlighting his contributions to lichenology, is included in the chapter on the nine Presidents of the International Association for Lichenology. Jahns played an important role during the past 40 years with his highly influential book, co-authored by Aino Henssen, entitled Lichenes. Eine Einführung in die Flechtenkunde. He is well-known for his extensive work and numerous publications on lichen morphology and ontogeny, particularly the development of fruiting bodies in different genera.