We use the term microbiome to describe the totality of all microorganisms – for example bacteria, viruses or yeasts – on earth. In humans, we find the microbiome in different forms in the respiratory tract, in the gastrointestinal tract, on the skin and in the genital tract. These microorganisms live with us in symbiosis, fending off pathogenic germs and supporting the functions of our body. The composition of the microbiome changes throughout our lives. It is sensitive to various disturbances such as an unbalanced diet, medications and various environmental factors. Numerous diseases are associated with an altered gut microbiome. New research findings give us hope that in the future we could use the microbiome as a novel therapy to treat a wide variety of diseases.