An easy-to-understand and comprehensive guide to gut bacteria featuring new research studies. New 3rd edition. This guide has been writeen by microbiologists and is meant for everyone who is interested in gut and oral microbiotas. It offers concrete examples of the connection between different disorders and microbiota. It also helps examine one´s own gut health and its linkage to different diets. The foreword about the operation of the gastrointestinal tract, common disorders and clinical methods has been written by the specialist in Internal Medicine and Gastroenterology, Jari Koskenpato, M.D, Medical center Aava.