Multiyear ice is quite thick in general, and it needs to be distinguished from thinner types of ice because it represents a severe navigational hazard. Here, models are described for the radar backscatter from multiyear sea ice, based on simple scattering layers. Under cold conditions, the radiative transfer volume-scatter model can describe the backscattering from multiyear ice for frequencies higher than about X-band, while the surface scattering contribution has to be included for lower frequencies. A simple semi-empirical model is shown to be a good approximation to the radiative transfer model in describing the volume scattering from multiyear ice.