The research described in this thesis focuses on improving our understanding of the behaviour of reinforced concrete masonry subjected to shear. All shear design methods in current masonry building codes are empirically based, and have been shown to produce widely varying predictions of shear strengths of masonry walls, beams and columns. Furthermore, the research community acknowledges that there is little to no consensus on the exact mechanisms of shear transfer in masonry elements, thereby slowing the replacement of empirical design expressions with more rational approaches. Given that shear failures can be brittle and sudden, with little to no warning of impending failure; experimental research focusing on these two issues is of primary importance.An extensive experimental program consisting load-testing fifteen large-scale reinforced masonry beams is presented in this thesis. The results definitively show that principles that ix