Dysplasia, or intraepithelial neoplasia, consists of noninvasive neoplastic cellular proliferation that may precede or accompany invasive neoplasia. Diagnosis is mainly based on histological criteria, which include cytological and structural alterations, since macroscopically identifiable lesions often do not occur. In all current classifications, dysplasia is divided in two categories, low- and high-grade, with the aim of attempting to evaluate risk and guide the therapeutic approach. The classification of the Vienna consensus aims to unity criteria and decrease interobserver variability in diagnosis. In the digestive tract, evaluation of epithelial dysplasia is especially important in four entities: Barrett's esophagus, chronic gastritis, inflammatory bowel disease, and colorectal adenomas. The criteria for diagnosis and dysplasia staging are the same in all these entities, but the therapeutic approach may vary according to the affected organ and the clinico-pathological context.