Understanding the shear performance of polymer matrix composites (PMCs) using a multiscale methodology requires novel in situ experimental techniques at each length scale. One limitation of the multiscale paradigm is inadequate experimentation at the microscale. In addition, limited investigation exists at the mesoscale to understand progressive damage phenomena. And lastly, although new experimental methods are required for in situ damage prognosis, many still need to provide the means of standardization. This study provides basic knowledge of microstructural instabilities, mesoscale damage prognosis, and the influence of size effects on PMCs while under shear loading