Over the past several years, a wealth of experimental evidence concerning the structure of simple grain boundaries (GBs) in metals has accumulated which suggests that the GBD/SU description of GB structure is applicable, at least at some level, to GBs in general. According to this model, high-angle GBs contain intrinsic arrays of grain boundary dislocations (GBDs) possessing Burgers vectors (b) which are translation vectors of an appropriate DSC-lattice, arranged in a network which is consistent with Frank's formula.A special property of secondary GBDs (SGBDs), i.e., GBDs possessing bs which are not lattice vectors of either of the adjoining crystals, is that a step in the boundary plane is often associated with their core.