Barrier-system dynamics are a function of antecedent topography and substrate lithology, Relative sea-level (RSL) changes, sediment availability and type, climate, vegetation type and cover, and various aero- and hydrodynamic processes during fair-weather conditions and extreme events. Global change has an influence on many of these drivers. Accelerating eustatic sea-level rise modifies the speed and direction of RSL change and reduces the return period of extreme events, changing rainfall and vegetation patterns alter river-discharge characteristics, shifting and strengthening ocean-current and wind patterns are reflected in increased storminess, and anthropogenic activities have reduced the natural supply of sediment to barriers. Many barriers, especially those fringing mid-latitude coastlines, are densely populated and protect areas of great economic value. In light of their vulnerability to flooding and hurricane-force winds, and given the increasing impact of residential, industrial and recreational development, sound coastal-zone management is essential.