Intolerance of gluten containing cereals (wheat, rye, and barley) is an etiopathogenetically heterogeneous and relatively common problem of modern man. It occurs as an adverse immune-mediated condition in genetically predisposed individuals. According to the pathogenetic mechanism of intolerance to the components of these cereals, it is classified into celiac disease as an autoimmune disease, wheat allergy as an allergic disease, and non-celiac gluten sensitivity as a non-autoimmune and non-allergic disease. Each of these disorders is characterized by specific intestinal and/or extraintestinal manifestations, which resolve on a gluten-free diet. This review article presents the basic characteristics of these disorders in accordance with modern knowledge.