Diagnosis of dentin hypersensitivity involves holistic assessment of the sufferer, particularly the condition of the involved tooth and to identify the cause of the pain or discomfort in order to prescribe appropriate treatment. Knowledge of the physiology of pain and methods of interpreting it with available clinical diagnostic devices is essential to reach a proper diagnosis. The history of the patient’s pain is the first clinical data the dentist must collect and consider with careful attention being paid to its characteristics as revealed by the patient’s responses, such as the type, duration, frequency, stimulating factors, and disturbed oral functions. Associating patient’s features and other factors capable of exposing dentin and opening up the tubules must be well explored. Ultimately, correct diagnosis necessitates awareness of clinical conditions which are similar in their presenting features. Diverse standardized stimuli and means of quantifying the pain of dentin hypersensitivity are discussed in this chapter.