When you hear the word microbiome, the chances are you will think of the gut. But the microbiome is so much more, namely the total of all microorganisms living on and in the human body. Skin, lungs or the digestive system, the mouth, throat, nose or the genital tract: they are all home to tiny living organisms such as bacteria, viruses or fungi. When the balance is correct, they are beneficial to human health. But what does the ideal microbiome look like? And what influence do quintillions of invisible organisms have on human health and disease?