The effect of grain size and deformation temperature on the behavior of wire-drawn a-Ti during compression has been examined. At strains of 0.3, the flow stress exhibited a negative HallPetch slope. This is proposed to result from the prevalence of twinning during the compressive deformation. Electron backscattered diffraction revealed that f10 " 12g was the most prolific twin type across all the deformation temperatures and grain sizes examined. Of the twinning modes observed, f11 " 22g twinning was the most sensitive to the grain size and deformation temperature. The range of morphologies exhibited by deformation twins is also described.