The main results of many years of research in the area of degradation and breakdown of thin (5 to 20 nm) silicon dioxide films are reviewed. The principal characteristics of the phenomenon are discussed: the actual meaning of intrinsic breakdown and its relation with the degradation of the oxide, the statistical nature of breakdown, the behavior under dynamic stresses, the existence of different modes, and the requirements for accelerated testing procedures for reliable extrapolation to operation conditions. Finally, a section is dedicated to the simulation of degradation and breakdown for computer-aided reliability tools. Copyright (C) 1996 Elsevier Science Ltd.