Annealing twins occur frequently in materials of low stacking fault energy, depending on the material processing. Where twinning is widespread, multiple or higher order twinning occurs. Experimental evidence, acquired by electron back-scatter diffraction (EBSD) from alpha brass and a nickel-based superalloy, is presented to demonstrate some of the factors which govern twinning. These findings have important consequences for the microstructural evolution of low stacking-fault energy alloys.