The chapter discusses the post-glacial re-colonization of European biota, focusing on the genetic consequences of climate change and the expansion of species from southern refugia. The study of palaeo-climates has advanced significantly, particularly the Pleistocene ice ages, which significantly modified species ranges. The last ice age and rapid post-glacial colonization of Europe are summarized, with a focus on the population genetic consequences of expansion from southern refugia and the retention of genetic diversity in these regions. Recent case studies using DNA sequence information have detailed the genetic variation and subdivision of species across Europe, including grasshoppers, hedgehogs, oak trees, black alder, brown bears, newts, shrews, water voles, silver fir, and house mice. These studies confirm that southern peninsulas of Europe were major ice age refugia, and most species emerged genetically distinct from these refugia. The refugial genomes contributed differently to the re-colonization of Europe, with three broad patterns—‘grasshopper’, ‘hedgehog’, and ‘bear’—defined by different expansion patterns and the formation of hybrid zones. The genetic data show a reduction in diversity from southern to northern Europe, associated with rapid expansion northward and varied topography in southern refugia. Some species have been diverging in refugial regions for a few ice ages, while others show more ancient separation. The chapter also discusses the use of suitable DNA markers, such as mitochondrial DNA (mtDNA) and chloroplast DNA (cpDNA), for tracing lineage, routes of expansion, and identifying relevant refugia. Several case studies are detailed, including the meadow grasshopper (Chorthippus parallelus), European hedgehogs (Erinaceus europaeus and E. concolor), brown bear (Ursus arctos), black alder (Alnus glutinosa), oaks (Quercus robur and Q. petraea), shrews (Sorex araneus group), common beech (Fagus sylvatica), and others. These studies provide insights into the post-glacial expansion routes, refugia, and genetic structure of these species across Europe.The chapter discusses the post-glacial re-colonization of European biota, focusing on the genetic consequences of climate change and the expansion of species from southern refugia. The study of palaeo-climates has advanced significantly, particularly the Pleistocene ice ages, which significantly modified species ranges. The last ice age and rapid post-glacial colonization of Europe are summarized, with a focus on the population genetic consequences of expansion from southern refugia and the retention of genetic diversity in these regions. Recent case studies using DNA sequence information have detailed the genetic variation and subdivision of species across Europe, including grasshoppers, hedgehogs, oak trees, black alder, brown bears, newts, shrews, water voles, silver fir, and house mice. These studies confirm that southern peninsulas of Europe were major ice age refugia, and most species emerged genetically distinct from these refugia. The refugial genomes contributed differently to the re-colonization of Europe, with three broad patterns—‘grasshopper’, ‘hedgehog’, and ‘bear’—defined by different expansion patterns and the formation of hybrid zones. The genetic data show a reduction in diversity from southern to northern Europe, associated with rapid expansion northward and varied topography in southern refugia. Some species have been diverging in refugial regions for a few ice ages, while others show more ancient separation. The chapter also discusses the use of suitable DNA markers, such as mitochondrial DNA (mtDNA) and chloroplast DNA (cpDNA), for tracing lineage, routes of expansion, and identifying relevant refugia. Several case studies are detailed, including the meadow grasshopper (Chorthippus parallelus), European hedgehogs (Erinaceus europaeus and E. concolor), brown bear (Ursus arctos), black alder (Alnus glutinosa), oaks (Quercus robur and Q. petraea), shrews (Sorex araneus group), common beech (Fagus sylvatica), and others. These studies provide insights into the post-glacial expansion routes, refugia, and genetic structure of these species across Europe.