Transport barriers in the present stellarators are reviewed in comparison with those in tokamaks. Peculiarities of stellarator plasma structures are introduced in order to obtain a unified view of the barrier formation mechanism.Particular attention is paid toneoclassical (-driven) internal transport barriersthat are commonly observed in stellarators.Discussion is made about important aspects of structural formation; e.g. the formation or bifurcation mechanism of radial electric field and its causal link with the transport barrier, and effects of magnetic field configuration on the barrier formation.