The vital roles that intestinal fl ora, now called microbiota, have in maintaining our health are being increasingly
appreciated. Starting with birth, exposure to the outside world begins the life-long intimate association our microbiota
will have with our diet and environment, and initiates determination of the post-natal structural and functional
maturation of the gut. Moreover, vital interactions of the microbiota with our metabolic activities, as well as with the
immunological apparatus that constitutes our major defense system against foreign antigens continues throughout
life. A perturbed intestinal microbiome has been associated with an increasing number of gastrointestinal and
non-gastrointestinal diseases including Clostridium diffi cile infection (CDI). It has become recognized that fecal
microbiota transplantation (FMT) can correct the dysbiosis that characterizes chronic CDI, and effect a seemingly
safe, relatively inexpensive, and rapidly effective cure in the vast majority of patients so treated. In addition, FMT has
been used to treat an array of other gastrointestinal and non-gastrointestinal disorders, although experience in these
other non-CDI diseases is in its infancy. More work needs to be done with FMT to ensure its safety and optimal route
of administration. There is a conceptual sea change that is developing in our view of bacteria from their role only as
pathogens to that of being critical to health maintenance in a changing world. Future studies are certain to narrow the
spectrum of organisms that need to be given to patients to cure disease. FMT is but the fi rst step in this journey.