The human gut hosts trillions of microorganisms. There is a vast diversity within the gut microbiota. The complex microbial communities that reside on or within the human body have a vital role in health and disease.

Testament to the importance of the gut microbiota in human disease is the growing number of conditions recently linked to symbiosis of the resident microbiota, including, amongst others, IBD, cancer, obesity, neurological disorders, ASD, pregnancy, dementia and cardiovascular disease. As we come to accept the gut microbiota as a human microbial 'organ' central to human health and disease, understanding the host–microbiota relationship is vital and targeting the gut microbiota is likely to become a future therapy for a number of conditions. Just how we can manipulate the resident gut microbiota to our benefit is yet to be fully determined, but new insights are emerging rapidly.