Electrical power systems rely on effective insulation. A better understanding of the processes leading to breakdown is essential in improving overall reliability. The authors attempt to explain the breakdown phenomenon in general based on the observations made with dielectric liquids. It is concluded that electrical breakdown involves a sequence of rather complex events. Although its occurrence can be delayed by various means, even the best systems will eventually fail. It is thus important to be able to predict the imminence of the breakdown and to develop warning systems which will enable one to alert the users and to adopt corrective measures