The response of the magnesium alloy, AZ61 to shock loading has been investigated in terms of it's Hugoniot (Equation of State) and variation of shear strength with impact stress. Comparison of the Hugoniot with that of the similar magnesium alloy AZ31 shows very little difference, and hence gives us confidence in our results. Measurement of the lateral stress shows a decrease behind the shock front which suggests a degree of time dependent hardening. Similar results have been observed in fcc metals, corresponding to observed increases in dislocation density in recovered samples. © 2009 American Institute of Physics.