The Polar Earth Observing Network (POLENET) multinational consortium has begun deployment of new networks of in situ sensors in the Arctic and across Antarctica for the International Polar Year (IPY). Two major networks of continuous GPS stations are being deployed for IPY as components of POLENET, funded by NSF and international partners. In Greenland, the GNET CGPS array consists of 24 stations deployed in 2007, with an additional 28 stations planned for deployment in 2008. The West Antarctic component of POLENET will consist of 32 CGPS stations; 16 of these will be co-located with broadband seismic sensors. Each CGPS station has Iridium communications to transfer data daily to the UNAVCO archives. These new networks will provide synoptic measurements around the entire perimeter of Greenland and across the interior of West Antarctica, allowing refinement of estimates of recent ice mass change of the Greenland and West Antarctic Ice Sheets. We will measure the steady vertical velocity field due to isostatic rebound with GPS and constrain earth rheology (elasticity, viscosity) through seismic studies. Both the viscoelastic response, constraining mass change since the Last Glacial Maximum, and the elastic response, resulting from recent mass changes, including major accelerations in ice loss or gain, can be modeled from continuous GPS measurements. The new in situ measurements will provide an accurate 'PGR correction' for GRACE, improving the GRACE-based estimates of ice mass changes in Greenland and West Antarctica. The CGPS measurements can be used to 'weigh' annual and interannual changes in ice mass with better spatial resolution than GRACE using Earth's instantaneous elastic response to surface load changes. Additional CGPS measurements conducted by POLENET partners will provide data from the Antarctic Peninsula, East Antarctica, and portions of the Arctic. A subset of the CGPS and seismic stations are intended to remain in place after IPY, providing a legacy in observational infrastructure in the polar regions and in the technological capability for autonomous operations in extreme environments.