This chapter provides a review of Cenozoic plant assemblages from the sub-arctic North Atlantic region and their biogeographic implications. Previous work is reviewed and new data are presented that considerably change our understanding of the role of the northern North Atlantic for plant dispersal and evolution of plant lineages during the Paleogene and Neogene. Paleogene plant fossils in this region are known from West and East Greenland, the Faroe Islands and Scotland. In contrast to the widely held view that most Paleogene plant taxa of Greenland belong to extinct lineages, we provide evidence for the presence of several extant genera in these floras (e.g. Fagus, Quercus). Thus, Engler’s hypothesis about the ‘Arcto-Tertiary element’ remains a fundamental hypothesis about the origin of northern temperate tree genera. In general, a remarkable diversity of extinct and modern lineages of Fagaceae is documented for Palaeocene and Eocene floras. Neogene fossils are found in Iceland and provide records of climate evolution in the sub-arctic North Atlantic and of the duration of a functioning land bridge for plant migration between North America and Europe. Counter to the traditional view suggesting a functioning land bridge only during the Paleogene, there isnow convincing evidence that this link was available for plants until the latest Miocene. This has important implications for understanding low genetic differentiation documented in extant plant groups having a disjunct distribution in northern temperate regions of Europe, North America and East Asia. Relatively warm conditions persisted in the sub-arctic North Atlantic until the end of the Zanclean (early Pliocene) based on plant fossil evidence from Iceland. The shift to modern tundra conditions occurred during the Piacenzian (late Pliocene) and is documented in the Pliocene and Pleistocene fossil plant assemblages of Iceland.