Global sea level has fluctuated significantly in the past, over glacial and inter-glacial time scales. Such variations arise from the slow buildup and even more rapid collapse of major ice sheets, including the present day Greenland and Antarctic Sheets. In this presentation mechanisms of ice sheet collapse are reviewed and implications for society over the next century and beyond are explored. Both ongoing observational and computational efforts aimed at addressing sea level change are surveyed. Areas for scientific advance are discussed.