Relict species or populations mostly occur in small and isolated habitats and are remnants of wider distributions in the past. The recent situation of such populations, which have often been scattered along the periphery of the distribution range over long time periods, has led to independent evolutionary processes. These are reflected today in morphologically and genetically unique characteristics that occur exclusively in these populations. Such evolutionary lineages caused by long-term isolation are often described as “evolutionary significant units”; the theory emphasises the distinctiveness of locally restricted phenological, morphological, and/or genetic units. Furthermore, these differentiation processes represent an important evolutionary potential, which distinguishes relict populations from the populations of the main distribution. This evolution in relict populations may in some cases be of high value for the future adaptiveness of the species concerned. On the other hand, very isolated relict populations often also suffer from repeated bottlenecks and the negative effects of genetic drift which enforce the evolution of local uniqueness, but cause losses of genetic diversity on the taxon and intraspecific level. Thus, ecological selection acts much more strongly and therefore more quickly in small and isolated remnant populations than in core populations. Furthermore, populations at the edge of the species’ distribution are often exposed to ecological conditions that are different from those in the core area. This selection under different habitat conditions can lead to new allele combinations essential to survival under conditions which differ from those of the core area; they may therefore be relevant for responses to the challenge of future climate changes. Following the contributions presented in this book, we conclude that peripheric populations are of particular importance for conserving the complete evolutionary and adaptive potential of species and their intraspecific variability in terms of the Convention on Biological Diversity.