Superplastic behaviour and isostatic diffusion bonding (DB) have been investigated for as-received annealed Zircaloy-4 sheet of relatively large grain size. The material was superplastic at strain rates up to 5.0 x 10(-4)s(-1) at temperatures in the lower part of the alpha+beta phase field for beta -phase volumes of 10-20%. At higher strain rates and lower temperatures the material deformed by power law creep. The DB studies showed that for intermediate and higher temperatures in the alpha+beta phase field, sound bonds could be obtained at relatively low pressures and short times. Bonding in the alpha -phase field required much higher pressures. Modifications to an earlier model of the DB process involved constraint of collapse by creep of inter-void ligaments at the bond interface. This lead to a dominance of stress directed boundary diffusion and gave improved agreement between prediction and observation for DB of the alpha- phase.