Microbes can now be found in nearly every niche thehuman body offers. However, the complexity of the microbiota of a given sitedepends on the particular environmental condition thereof. Only microbes whichare able to grow under these conditions, will prevail. Recent publicationsimply that the microorganisms do not only have multiple, critical consequencesfor host physiological processes such as postnatal development, immunomodulationand energy supply, but also effects on neurodevelopment, behavior andcognition.Within this book we will focus on the techniquesbehind these developments, epigenomics and on the various parts of the human body which are inhabited by microorganism such as the mouth, the gut, the skin andthe vagina. In addition, chapters are dedicated to the possible manipulationsof the microbiota by probiotics, prebiotics and faecal transplantation.