The impact of climate change, and particularly rising sea levels on shallow fresh groundwater lenses, is widely regarded as a major challenge to the sustainability of ow-lying island countries. Recent research, however, has shown that over 88% of atoll islands in the Pacific and Indian Ocean are counter-intuitively either stable or increasing in land area. During major ENSO events, sea level changes of up to 0.4m above and below normal levels have been observed. Whether atoll reef systems will continue to cope with increasing temperatures and ocean acidification is a critical question. Climate model projections of changes in drought severity and frequency are of generally low confidence because, ENSO events, key drivers of drought in the Pacific, are not well described by climate models. This work reviews both climate change projections and observed impacts on groundwater hydrology in atoll countries in the Pacific. Changes in evaporation requires further work. Greatest vulnerability is to changes in recharge rates, groundwater extraction and island overtopping. Increasing population densities, growing water demands, inadequate sanitation and poor water and sanitation governance are more immediate threats. The best adaptation strategy appears to be overcoming the current challenges by building on the recognised strengths and resilience of island communities, strengthening institutional structures and human resources while maintaining and enhancing the integrity of island ecosystems, as Barnett has concluded, and investing in education and training at all levels.