A particular characteristic of an explosively produced weld is that the profile of the weld interface often has a regular wavy appearance. During the last decade several authors have postulated mechanisms by which these waves are produced and have attempted to correlate their theoretical predictions with available experimental data. As yet, however, there is no consensus of opinion on the particular mechanism which is actually responsible for the waves and indeed several of the mechanisms referred to are mutually contradictory. After discussing briefly some of the theories which have been proposed, one of them, the vortex shedding mechanism recently described by Kowalick and Hay5, is examined in more detail. An account is given of some theories and observations of vortex shedding alternative to those used in ref. (5) in an attempt to identify an area which might eventually lead to both a quantitatively and qualitatively accurate description of the mechanism producing the interface waves.