Fatigue crack initiation and propagation in aluminium butt welds has been investigated. It is shown that the initiation of cracks from both buried defects and from the weld reinforcement may be quantified by predictive laws based on either linear elastio fracture mechanics, or on Neuber's rule of stress and strain concentrations. The former is preferable on the grounds of theoretioal models of crack tip plasticity, although either may be used as the basis of an effective design criteria against crack initiation. Fatigue lives fol1owing initiation were found to follow predictions based on the integration of a Paris type power law. The effect of residual stresses from the welding operation on both initiation and propagation was accounted for by a Forman type equation.This incorporated the notional stress ratio produced by the residual stresses after various heat treatments. A fracture mechanics analysis was found to be useful in describing the fatigue behaviour of the weldments at incrodsed. temperatures up to 300°C. It is pointed out however, that the complex interaction of residual stresses, frequency, and change in fracture mode necessitate great caution in the application of any general design criteria against crack initiation and growtn at elevated temperatures.