Liquid metal embrittlement is the reduction in the elongation to failure that can be produced when normally ductile solid metals are stressed while in contact with a liquid metal. This review describes its principal characteristics and the several models which have been advanced in attempts to explain the occurrence and different features of the process. Comparison between theory and experiment indicates that many, but not all, of its aspects are consistent with a mechanism which operates by reducing the fracture surface energy of the solid metal. Literature reports show that liquid metal embrittlement can occur with a very wide range of material combinations, and while most of the data refer to laboratory studies, it is clear that the phenomenon is also of technological significance as a potential cause of plant damage.