This is a large-scale observational study aiming to evaluate the long-term effectiveness and safety of Fecal Microbiota Transplantation (FMT). FMT is a procedure that transfers gut bacteria from healthy donors to patients to restore a balanced gut microbiome. The study will follow approximately 4,000 patients who have received or will receive FMT for conditions like recurrent C. difficile infection, inflammatory bowel disease, functional gastrointestinal disorders, and certain neurological conditions. The main goals are to: * Assess the disease remission rates at 3 months, 1 year, and 5 years after FMT. * Monitor the long-term safety and any potential side effects. * Identify factors that may influence how well a patient responds to the treatment. This research will use both existing patient data (retrospective cohort) and newly collected data from future patients (prospective cohort). The findings are expected to help improve and standardize FMT treatment for better patient care.