In configurations with transport barriers the improved edge andcore confinement leads to a large pressure gradient and largeedge bootstrap current density which often drivemagnetohydrodynamic (MHD) instabilities terminating thedischarge or reducing the discharge performance. The edge andthe core transport barriers deteriorate or are completely lost.In this paper, recent experimental and theoreticaldevelopments concerning MHD instabilities occurring near/at theedge and the core transport barriers are summarized emphasizingthe dominant instabilities and the comparison with theory.