Extensive field studies on the African and North American plates during this past decade have yielded a wealth of new data and ideas about rift basins and the origin of passive margins. New surface and subsurface basins have been identified; fossils abound in strata that only recently were considered barren; oil exploration is being actively pursued in continental strata of the Richmond-Taylorsville, Sanford and Newark basins, Late Triassic marine strata have been identified in Georges Bank off the coast of Massachusetts, and the roles of wrench tectonics, successor basins and listric normal faults have challenged the classical view that these are simple extensional basins. This two part work brings together representative examples of these studies. It is not intended as an exhaustive synthesis of the subject, but rather a vehicle to present new data, new ideas and alternative views. Some of the papers present regional summaries, others attempt to relate local features to regional questions, while others describe modern rift basins as possible analogs of early Mesozoic basins.