This paper summarizes the results of some recent research on a thermomechanical method of refining the grain size in precipitation hardenable aluminum alloys and illustrates the infuence of grain refinement on several material properties. Grain refinement is achieved by deliberately introducing a large number of nucleation sites for recrystallization and by controlling grain growth after recrystallization. Recrystallization to a relatively small and equiaxed grain size has been achieved in a number of commercial aluminum alloys using these concepts. The influence of the fine recrystallized grain size on such properties as superplastic deformation, room temperature tensile properties, fatigue life, and exfoliation corrosion resistance is discussed. The results show that refinement to a grain size of 8–14 µm is sufficient to develop extensive superplasticity and to yield a small increase in tensile properties in alloys such as 7075 and 7475.