Thermodynamic and kinetic aspects of interfacial decohesion are analyzed for a uniformly stressed interface in the presence of an embrittling impurity. During the interfacial separation, the impurity penetrates into the interface and reduces it cohesion. Rice (1976) and Hirth and Rice (1980) analyzed the thermodynamics of this process in great detail with emphasis on the limiting cases of infinitely fast and infinitely slow separation. The 'dynamic' model of decohesion proposed in this work extends their analysis to an arbitrary relation between the rates of separation and impurity transport to the interface, including transient kinetics in which the two rates are comparable to one another. Such kinetics play an important role in the phenomenon of dynamic embrittlement observed in many materials. Calculations of dynamic decohesion have been performed for two mechanisms of impurity supply to the interface: the reaction kinetics and bulk diffusion. In both cases a kinetic parameter R has been identified such that R 1 for slow separation, R 1 for fast separation, and Rΰ·1 for the transient regime. In the transient regime, the work of decohesion, cohesive strength, the impurity concentration at the new surfaces, and other properties depend sensitively on the strain rate in agreement with experimental observations of dynamic embrittlement.