The influence of the solid earth on the dynamics of ice sheets has crucial implications for climate change and sea-level rise. Projections of ice sheet retreat and sea level rise are heavily influenced by solid earth properties such as basal heat flow, bed properties, lithospheric thickness and mantle viscosity.    Recently installed seismic networks in Antarctica and developments in technology allowing year-round unattended seismograph operation even in the coldest regions now allow us to use seismology to investigate these interactions.  We use seismic velocity maps to constrain parameters important for ice sheet models such as heat flow and mantle viscosity.   Inferred mantle viscosity is lowest beneath Marie Byrd Land and highest beneath East Antarctica, and the variation is large enough to have a first order effect on glacial isostatic adjustment (GIA).   Inferred mantle viscosity in West Antarctica is much lower than assumed in recent GIA models, and limits the GIA response to ice sheet mass changes to the last several hundred years, and leading to poor prediction of uplift observed by GPS.  The Transantarctic Mountains lie along a first order boundary in mantle viscosity, probably leading to a complicated GIA response poorly modeled by 1-D viscosity models.    West Antarctica shows low mantle seismic velocities associated with late Cenozoic rift systems and with a large mantle thermal anomaly supporting the Marie Byrd Land dome.   These structures suggest high geothermal heat flow may have a first order effect on glacial dynamics in West Antarctica, as indicated by recent high heat flow measurements from the WAIS ice core.   In addition, the recent discovery of deep-long period volcanic earthquakes beneath the ice sheet in Marie Byrd Land demonstrates the existence of active subglacial magmatic systems and suggests volcanic eruptions may have an important effect on the ice sheet.