Variation in DNA macromolecules is used to infer not only the phylogenetic history of a species but also the recent evolutionary and demographic history of populations within a species or among closely related species. The latter is a subject of the fi eld of phylogeography, established by Avise et al. (1987), which uses genetic information to study the geographic distribution of genealogical lineages, especially those found within species. The fi eld of phylogeography has managed to successfully bridge the gap between macroevolution (phylogeny) and microevolution (population genetics) and presents a unifi ed frame of the evolutionary processes. The major goals of phyloegeography are to decipher spatial and temporal components of population structure and to interpret the evolutionary and ecological processes responsible. Based on appropriate sampling of individuals and genes, phylogeographers can be in a position to test biogeographic hypotheses, describe the evolution of reproductive isolation of population units, and infer processes underlying the origin, distribution and maintenance of biodiversity. Given that the structure of population genealogies is infl uenced by demographic history, phylogeographers can also make inferences about temporal changes in the physical and biotic environment of a population using present-day genetic data (BeheregarayInstitute of Marine Biology, Biotechnology and Aquaculture, Hellenic Centre for Marine Research (HCMR), P.O.Box 2214, 71003 Heraklion, Crete, Greece. Email: kasapidi@hcmr.gr2008). The exponentially increased number of phylogeographic studies that have been carried out have elucidated aspects of the evolutionary history of species that have been previously unnoticed, such as the presence of barriers to gene fl ow which could be related to major paleogeographical events, the existence of refugial populations during the glacial ages and their postglacial expansion routes (e.g., Taberlet et al. 1998), demographic changes such as population bottlenecks or expansions, the presence of distinct evolutionary clades or even cryptic species.