The available studies of the creep behaviour of AZ91 alloy produced by die casting, ingot casting, or thixoforming are reviewed in the present paper. Differences in microstructure and creep response are analysed and discussed with a view to providing a unitary, comprehensive description of the creep behaviour of this material. In particular, the minimum creep rate dependence on applied stress is described by means of a modified form of power law, which takes into consideration the effects of grain size and of intragranular precipitates interacting with dislocations. Analysis of the data obtained from the die cast alloy indicates that, in this material, creep is controlled by climb. Based on this observation and on theoretical considerations, as well as on the microstructural similarities, it is concluded that creep is controlled by climb also in thixoformed and ingot alloys. The effect of grain size is then quantified, and the strengthening effect of intragranular precipitates is described by introducing the threshold stress concept.