A detailed reappraisal of the computer modelling of the rare-earth fluorides is presented. A new set of interionic potentials is obtained by empirical fitting to crystal structural data alone. These potentials are then tested by calculation of elastic and dielectric constants, whose values agree favourably with those measured experimentally. Calculations are then presented of the basic defect formation energies for each material, and predictions of the expected type of intrinsic disorder made.