The interview is a crucial part of a medical evaluation. It is a conscious, goal-oriented conversation between a patient and/or parent and a clinician. Effective interviewing is necessary to appropriately identify and evaluate intellectual and developmental disorders. Skillful interviewing improves the quality of the information obtained, strengthens the relationship between the patient and the clinician, and improves compliance to recommendations. This entry discusses general strategies for successful interviewing, reviews key components of the medical history, and concludes with a discussion of diagnosis and treatment.