Ice is a highly viscous material which deforms slowly under stress. The force balance is described with the Stokes equations, and the constitutive relationship between stress and strain is generally non-linear, temperature dependent and anisotropic. Ice is hence a challenging material to model, and the system of equations is typically solved using a variety of approximations. Data from InSAR and ground-penetrating radar studies can be used to constrain the boundary conditions (e.g. surface mass balance, ice thickness) and to control the modeling output (e.g. by comparing the modelled isochrones with internal radar layers). For the most recent applications I have used the full Stokes, finite element software Elmer/Ice.