Because of the low symmetry hexagonal close packed atomic structure of Mg there are a limited number of deformation mechanisms to accommodate deformation along the crystallographic c-axis. Only one dislocation slip based mechanism can accommodate deformation along the c-axis. Therefore, deformation twinning plays a dominant role in the accommodation of deformation along the c-axis. To date there have been a number of studies to examine twinning but there are still a number of critical details that need to be addressed to properly inform modeling efforts. Shown below are the first in-situ images of twin propagation of single crystal magnesium, images captured by Vignesh Kannan at Johns Hopkins University. From these images insight is gained towards the kinetics of twinning and nucleation sites during strain accommodation. Corresponding microstructural analysis elucidates the formation of secondary twins (twins within twins) at small scales that not previously been observed.