The aim of this book is to present the newest trends in genetic studies conducted in Poland and concerning variability in populations, variability studied on various levels of its organization. The works presented deal with widely understood problems of populational genetics, ecological genetics, evolutionary biology, processes of adaptation, speciation and taxonomy. Rapid progress in the develpment of research methods and techniques, based on use of various markers, including molecular ones in studies of variability significantly expanded possibilities of tracing the phenomena taking place in populations. Such research approaches offer a new perspective, which makes possible better understanding of genetic processes in populations and on the level of a species.