Interpretation of factors responsible for land-sea level change in areas such as the Great Barrier Reef involve an appreciation of not only the field evidence purporting to show change, but also the theoretical models which attempt to explain depth variations in shorelines of a given age. Relative movements in sea level in Holocene time may result from a number of factors operating either external to the study area (e.g. glacio-eustatic, and broad-scale hydro-isostatic deformation of the globe resulting from the last deglaciation and sea level rise), or those whose effects are essentially local (e.g. changes in circulation and tidal levels within partially enclosed water bodies induced by sedimentation or biogenic reef growth, meteorological changes affecting the magnitude and frequency of storminess, regional flexures and/or faulting, and hydro-isostatic deformation of shelves and adjacent coasts accompanying the Postglacial Transgression). In this paper, data from the northern Great Barrier Reef Province are evaluated in relation to various causes of sea level change. Emphasis is placed on explaining variations in relative sea level position by hydroisostatic theory. Deflexion in the ocean margin ‘hinge zone’ varies with continental shelf geometry and rigidity of the underlying lithosphere. The fact that the oceanic crust meets the continental crust quite abruptly east of the study areas, dictates that moderately strong flexures occur, and that variations in Holocene hydro-isostatic flexure in the Great Barrier Reef Province are partly explainable in these terms.