A method is presented for determining the dynamic shear behaviour of brain tissue using a rotational plate-plate rheometer in a strain and frequency range representative for impact conditions. The non-linear strain behaviour was characterised using shear stress relaxation experiments and expressed in terms of a damping function. Results were corrected for the non-homogeneous strain field applied. Brain tissue was found to exhibit shear softening (45% at 20% strain) that could be fitted with a second order Mooney-Rivlin model. The time dependent behaviour of brain tissue seems to be independent of the strain level. It was characterised up to 1000 Hz by small strain oscillatory shear experiments and application of the Time Temperature Superpositioning principle. The data presented can be used to fit a non-linear material model for brain tissue under shear loading for frequencies up to 1000Hz and strains up to 20%.