Melting of the Greenland and Antarctic ice sheets is accelerating and the resulting fresh water input into the oceans will be the dominant contribution to future sea level rise as the Earth’s climate changes. The PISCEES project is developing better computer models of large ice sheets to improve future sea level rise projections. In particular, multi-scale formulations of ice sheet dynamics are being implemented to represent the wide range of spatial scales in a robust, accurate and scalable manner. In addition, PISCEES scientists are creating new tools and techniques for validating ice sheet simulation results against observations and providing estimates of the uncertainty surrounding future projections.