Although the premise that uplift around the margin of an ocean might be balanced by subsidence beneath the ocean floor, which underpinned Darwin’s hypothesis, is now seen to be simplistic and flawed, his remarkable deduction that such subsidence would give rise to three types of reefs, fringing reefs, barrier reefs, and atolls, has been broadly validated by stratigraphy and dating of cores through atolls. There are numerous exceptions to this sequence of development, particularly for those reefs on continental margins or that have experienced uplift. Nevertheless, gradual subsidence characterizes ocean lithosphere as it migrates from mid-ocean ridge (spreading center) to ocean trench. Although fluctuations in sea level have punctuated the development of atolls, with periodic exposure and karstification of the carbonate platform, gradual subsidence has persisted with successive veneers of reef limestone added during each highstand. There seems little doubt that this powerful hypothesis can be extended to explain the broad evolution of many midocean atolls for which coring has not yet confirmed an underlying volcanic basement.