The Rome IV Diagnostic Questionnaires were developed to screen for functional gastrointestinal disorders (FGIDs), serve as inclusion criteria in clinical trials, and support epidemiological surveys. Separate questionnaires were developed for adults, children/adolescents, and infants/toddlers. For the adult questionnaire, we first surveyed 1,162 adults without gastrointestinal disorders, and recommended the 90 percentile symptom frequency as the threshold for defining what is abnormal. Diagnostic questions were formulated and verified with clinical experts using a recursive process. The diagnostic sensitivity of the questionnaire was tested in 843 patients from 9 gastroenterology clinics, with a focus on clinical diagnoses of irritable bowel syndrome (IBS), functional constipation (FC), and functional dyspepsia (FD). Sensitivity was 62.7% for IBS, 54.7% for FD, and 32.2% for FC. Specificity, assessed in a population sample of 5,931 adults, was 97.1% for IBS, 93.3% for FD, and 93.6% for FC. Excess overlap among IBS, FC, and FD was a major contributor to reduced diagnostic sensitivity, and when overlap of IBS with FC was permitted, sensitivity for FC diagnosis increased to 73.2%. All questions were understandable to at least 90% of individuals, and Rome IV diagnoses were reproducible in ¾ of patients after one month. Validation of the pediatric questionnaires is ongoing.