Eilif Dahl, noted lichenologist and student of Fennoscandian vegetation, was a generalist who applied a strong background in the physical sciences to considerations of ecological state and change. Dahl worked on both lichens and vascular plants; his earlier efforts were concentrated on taxonomy and floristics, but as time went on he increasingly integrated phytosociological theory and methods into his work, which ultimately extended to historical and phytogeographical interpretations. Typical of his approach were his defenses of the nunatak hypothesis (that ice-free “refugia” existed in Scandinavia even during the height of the Ice Age), which relied on his evaluation of both botanical and geological kinds of evidence. Another characteristic of Dahl’s work was his desire to provide explanations based on more than correlations: as evidenced, for example, in his connections of environmental conditions to physiological responses to explain the basis of species range limits. Dahl was also a committed conservationist who raised the issues of acid rain and global warming well before such worries had crossed the general consciousness. His legacy as a phytogeographer was assured by the posthumous publication of his great work The Phytogeography of Northern Europe in 1998.