In North America over the past four and a half decades Dr John W. Thomson has been 'Mr Arctic' in the world of lichenology. He has undertaken many Arctic expeditions himself and as a systematist has produced an impressive array of monographic treatments, many of which have dealt with Arctic genera. His life-long research on Arctic lichens culminated in the publication of The Arctic Lichen Flora, vol. I: The Macrolichens (Colombia Press) in 1984 and vol. II: The Microlichens (University of Wisconsin Press) in 1995. Together they are a major synthesis that will be a valuable guide for generations to come. It is thus highly appropriate that we dedicate the proceedings of this polar symposium to Dr J. W. Thomson, scholar.