Randomization and Intervention Phase. Upon completing the baseline assessment phase, participants will be randomized to one of 3 treatment groups. A customized computer program will be used to do the randomization in an adaptive manner that ensures the 3 groups remain fairly balanced with respect to possible important predictors of outcomes: age, sex, predominant stool pattern (alternating, constipation-predominant or diarrhea-predominant), and severity of IBS symptoms and psychological symptoms at baseline. When each new participant is randomized, the program will adjust the probabilities of assignment to the three groups so that there is a higher probability of assignment to the group that results in the best balance.