Although the phenomenon of lateral gene transfer has been known since the 1940's, it was the genomics era that has really revealed the extent and many facets of this evolutionary/genetic phenomenon. Even in the early 2000s with but a handful of genomes available it became clear that the nature of microorganisms is full of genetic exchange between lineages that are sometimes far apart. The years following this saw an explosion of genomic data, which shook the "tree of life" and also raised doubts about the most appropriate species concepts for prokaryotes. This book attempts to represent the many-fold contributions of LGT to the evolution of micro and, to an extent, macro-organisms by focusing on the areas where the Editor felt it had the largest impact: metabolic innovations and adaptations and speciation.