Electrochemical models of failure in oxide perovskite materials are reviewed. It is noted that oxygen vacancies are a common source of electrical degradation, fatigue, and ageing. Taking the behavior of oxygen vacancies into account, a semi-quantitative model for time dependent dielectric breakdown (TDDB) is proposed and a quantitative fatigue mechanism is discussed for ferroelectric thin films. Based on the fatigue theory, a recent improvement in fatigue of ferroelectric thin films is presented. Correlation between leakage current and fatigue is also presented.