Abstract A considerable body of data has been collected on the continental margins of the world but the greater part of these data are concentrated in a few areas and the remaining areas have received only limited attention. This is especially true of data dealing with the deep-seated structure. There has been a tendency to group the margins into Atlantic and Pacific types, characterized respectively by truncation of pre-Mesozoic structures or by a coincidence between the margins and Meso-Cenozoic orogenic belts but this classification now appears to be too simple. It would seem more appropriate to relate the margins to the manner of their development than to area or time. Characteristics of the deep structure of the transition zones have been determined from seismic refraction (D.D.S.) studies and it is obvious that their development is related to deep-seated physico-chemical changes. There is, however, sharp disagreement about the relative importance of horizontal and vertical movements in producing the features that can be observed today. Evidence of large scale subsidence is recorded in the sediments of present and fossil continental margins but compelling arguments for major horizontal movements can be raised on the basis of recent data from the ocean basins. Resolution of this problem will depend upon better correlation of marine and terrestrial geological and geophysical data and determination of the age and method of formation of the ocean basins.