According to some workers, ancient epeiric and mioclinal shelf seas should have lacked normal astronomical tides because of their shallow depths and great size. A variety of sedimentological and paleontological evidence, however, indicates that Precambrian, Cambrian, Ordovician, and Cretaceous strata of western North America, Carboniferous strata of the eastern United States, Precambrian and Cambrian strata of Scotland, and Precambrian and Ordovician strata of South Africa, which were, in part, deposited in such shallow seas, contain extensive tidalites. On Holocene continental shelves, a positive correlation exists between shelf width, tidal range, and tidal current velocity; the widest shelves are characterized by the greatest tidal ranges and the greatest tidal current velocities. This relationship is generally applicable to ancient epeiric and mioclinal shelf seas, and we conclude that ancient shallow seas were, in fact, characterized and dominated by tides and by tidal circulation patterns. Therefore, sedimentological and paleontological evidence of tidal influences should be sought more widely in strata that accumulated in such seas.