Sea ice plays a key role in the earth climate system as it controls the fluxes between ocean and atmosphere and drives the global circulation due to its seasonal cycle of melting and freezing. Ice covered oceans also govern the earth's albedo and, therefore, the atmosphere's energy flux.Although satellites provide information on sea ice extent and seasonal variability, very little is known about the thickness of the sea ice and its long term thinning or thickening.Electromagnetic methods are perfectly suitable for sea ice thickness measurements as the ice represents a resistive layer covering a highly conductive ocean. For more than ten years, the Alfred Wegener Institute uses active frequency domain EM devices to assess the spatial and temporal evolution of Arctic and Antarctic sea ice. For that purpose Geonics' EM31 has been towed with sledges on ice surfaces and suspended from the ship's bow crane for continuos measurements while steaming through sea ice. Since 2001 a purpose built helicopter EM system is operating from ships and land stations delivering a unique sea ice thickness dataset in space and time.A ramac GPR system was used on sea ice in March and October 2003 in the Arctic and Antarctic respectively. These campaigns where one of the first successful adoptions of the GPR technique on sea ice.