"Microorganisms constitute a very diverse group of organisms inhabiting various environments. They are characterized by various processes occurring at the genetic level and require a differentiated approach in genetic research. In the past, the traditional taxonomy was based on morphological markers which were not stable and change according to environmental conditions. DNA-based technology has generated a revolution in determining the identity and taxonomy of microbes, particularly in fungi. The emergence of metagenomics has opened new avenues for the identity and taxonomy of non-culturable microorganisms. The proposed book presents, on the one hand, fundamental issues related to the broadly understood genetics of microorganisms, the organization of genomes, and their differentiation. On the other hand, it presents detailed issues related to the methods of genetic research used in various groups of microorganisms, taking into account their taxonomy, methods of identification, and assessment of their diversity. The book is divided into five sections on genetic research of bacteria, fungi, viruses, viroids, phytoplasma, and protozoa. There is a diversity of representation of contributors from Europe, Brazil, Mexico, Egypt, India, Iran. The proposed book will be very useful for postgraduate and research students of microbiology, genetics, biotechnology and biology. It will be an essential reading for the students owing to the inclusion of basic and applied aspects"--