The market for wrought magnesium alloys has lingered around 5000 to 7000 tonnes per year for the past fifteen years or so, and this is partly because of deficiencies in our understanding of the microstructural behaviour which influences formability. This paper examines microstructural evolution in the magnesium alloy AZ31 during hot working. Compression tests were conducted on homogenised AZ31 at three true strain rates - 0.01 s(-1), 0.1 s(-1), and 1s(-1) - and five temperatures in 50degreesC intervals from 200degreesC to 400degreesC. In addition, strain rate jump tests were conducted between strain rates of 0.1 s(-1), and 1s(-1) at constant work hardening rate, both in the 'upward' and in the 'downward' sense. Compression tests to a strain of one yielded flow stress curves which are typical of a metal which undergoes dynamic recrystallization, and the presence of the phenomenon was confirmed by metallographic examination of specimens taken from interrupted tests. Twinning was also found to occur at low temperatures and high strain rates, and work hardening curves were found to display a region with little change in gradient, which seemed to confirm this. The strain rate sensitivity was found to decrease with temperature from a value of approximately 0.12 at 400degreesC to close to 0.02 at 200degreesC. Colour metallography was used to reveal gross orientation changes with deformation.