The actual FMT procedure will be performed in the majority of cases by colonoscopy. Other possible routes of administration are via nasogastric or nasoduodenal tube (with upper formulation), enema and frozen oral tablets. The current preferred route of administration is via colonoscopy, based on observation (no head-to-head) trials showing improved efficacy, but standards of care may change in the future. In all cases, the route of administration will be based on patient characteristics and preferences, not for purposes related to the study. In all cases, informed consent for the treatment will be documented as guided by the Food and Drug Administration (FDA). The patient will stop all antibiotics (including vancomycin or other antibiotics against C. diff) at least 2 days prior to FMT. For all administrations other than oral capsules, patients will perform a bowel preparation with 4 liters of Golytely or equivalent osmotic laxative split between the evening prior to the procedure and the morning of the procedure. In a minority of instances, especially for pediatric patients, the patient may be electively admitted to the hospital the night before, to monitor medical stability during the preparation, facilitate bowel preparation, and provide intravenous hydration. The bowel cleansing preparation is generally taken orally, though in rare instances must be administered via nasogastric or nasoduodenal (NG/ND) tube. Hospital admission and bowel preparation via NG/ND tube will only be performed if indicated as standard-of-care, not for purposes specifically related to the study.