Dentin hypersensitivity is a prevalent and common complaint in dentistry. Identification of the etiological and predisposing factors for dentin hypersensitivity is of prime importance in the diagnosis and treatment planning of this dental complaint. In order to have a clinical manifestation of dentin hypersensitivity, the dentin must be exposed to the oral environment. Dentin exposure results from one or more etiological factors that lead to loss of enamel and/or loss of cementum and overlaying periodontal tissues. Many dental and medical conditions have been linked to dentin hypersensitivity as etiological or predisposing factors. Some periodontal or restorative treatment may initiate the dentin hypersensitivity symptoms. In this chapter, we will shed light on all the etiological and contributory factors responsible for dentin hypersensitivity.