A review of MHD limits to tokamak operation in terms of current, density and pressure is given. Although the current and density limits in a tokamak usually lead to disruptive termination of the discharge, it is argued that these can be avoided by staying away from the respective limits. This is especially true since operation close to these limits is not really desirable, due to the decreased confinement at very high density and the high disruptivity at low q. On the other hand, the limit to plasma pressure set by Neoclassical Tearing Modes and Resistive Wall Modes is too low to guarantee economic operation of future fusion reactors. Therefore, active control of these two in-stabilities is now being studied. Noticeable progress has been made by NTM stabilisation with ECCD. Avoidance of NTMs and RWMs by tailoring saw-teeth and spinning the plasma, shows promising results. Also, experiments on direct RWM stabilisation by active coils are showing their first encouraging results.