Horizontal gene transfer is a major driving force in the evolution of many bacterial pathogens. The development of high-throughput sequencing tools and more sophisticated genomic and proteomic techniques in recent years has resulted in a better understanding of this phenomenon. Written by leading experts in the field, this edited volume is aimed at graduate students and researchers and provides an overview of current knowledge relating to the evolution of microbial pathogenicity. This volume provides an overview of the mechanisms and biological consequences of the genome rearrangements resulting from horizontal gene transfer, in both prokaryotes and eukaryotes, as well as overviews of the key mobile genetic elements involved. Subsequent chapters focus on paradigms for the evolution of important bacterial pathogens, including Salmonella enterica, Streptococcus pneumoniae, and Staphylococcus aureus. The influence of socioeconomic parameters in the dissemination of transferable elements, such as antibiotic resistant genes in bacteria, is also discussed.