In this paper the evolution of a technique for protecting a structure from earthquake attack is traced from its beginning through to its currently most effective form, and this form, the Base Isolation System, is compared to other currently available techniques. The influence of higher mode effects in base isolated multi-storey structures is investigated and shown to be of considerable significance in determining the shear forces in the upper levels of a structure. Because of these higher mode effects the responses of appendages on isolated structures, while still being less than those for appendages on unisolated structures, can be significantly larger than previous 1-D analyses had suggested. A standard set of distributions of inter-storey shear up a multi-storey structure is presented with each distribution being defined by a parameter which varies from zero to unity.