Thermal and electric breakdown processes in thin film insulators are discussed. Interpretation of the processes is greatly facilitated by using specimens with self‐healing breakdowns, cleared of weak spots. Thousands of breakdown tests can be carried out on such specimens. Thermal breakdown is initiated by an increase in the electrical conductance by joule heat; breakdown occurs at a definite voltage, which can be calculated with good accuracy. Electric breakdown can be initiated by the increase of the electrical conductance in a channel by a pulse, such as an electronic avalanche. Destruction arises by discharge of the electrostatic energy stored in the specimen through the channel. The incidence of breakdown is of a statistical nature. In contrast to concepts which assume a definite breakdown field, electric breakdown can occur in certain oxides over a wide range of fields. Breakdowns occur at a rate which increases quasi‐exponentially with field and also with temperature, e.g., in hafnium dioxide. Experimental results are examined in the light of existing breakdown theories. It appears that further theoretical and experimental work is needed for the interpretation of the oxide results.