The idea to compile and edit the book is the result of over a decade of work by the editor, Dr. Nava Dayan, on various projects related to skin barrier, innate immunity, microbiome, developing products, testing methods and paths of products to the market, both for pharmaceutical and the cosmetic industries. The book is a summary of current status of knowledge, research tools and approaches in skin microbiome, in health and disease. It contains the following categories: healthy skin microbiome and oral-skin interaction, skin microbiome observational research, skin microbiome in disequilibrium and disease, skin innate immunity, testing and study design, regulatory and legal aspects for skin microbiome related products. The 18 chapters of the book are written by carefully selected leaders in the academia, industry exhibiting extensive experience and understanding in the areas of interest.