Irritable bowel syndrome (IBS) is a heterogeneous group of conditions related to specific biologic and cellular abnormalities that are not fully understood. Psychological factors do not cause IBS, but many people with IBS also have anxiety or depressed mood, a history of adverse life events, or psychosocial stressors. Physicians must understand the fears and expectations of patients and how they think about their symptoms and should also respond empathetically to psychosocial cues. Anxiety related to the unpredictability of symptoms may have a greater effect on quality of life than the symptoms themselves. Patients in generally good health who have ongoing or recurrent gastrointestinal symptoms and abnormal stool patterns most likely have IBS or another functional gastrointestinal disorder. Patients who meet symptom-based criteria and have no alarm features may be confidently diagnosed with few, if any, additional tests. Patients may not completely understand the diagnostic process; asking about expectations and carefully explaining the goals and limitations of testing leads to more effective care. There is no definitive treatment for IBS, and recommended treatments focus on symptom relief and improved quality of life. Trusting patient-physician interactions are essential to help patients understand and accept an IBS diagnosis and to actively engage in effective self-management.