Disruptions lead to the largest operational electromechanical loads on the vessel, its supports, and the in-vessel components. In addition, plasma-facing components can be exposed to very high thermal fluxes during the plasma thermal quench and to high-energy runaway electron beams. Therefore, disruptions represent one of the most demanding design load cases for this and the next generation of tokamaks, and they will need to be always strongly ameliorated or totally avoided in a commercial power plant. An overview of the observations and of the analytical and experimental work on disruptions carried out at JET both during the Joint Undertaking and under the European Fusion Development Agreement is presented.