Although structures have been built from masonry for many years, little is still known about the behaviour of a wall subject to in-plane shear. This is particularly true of partially grouted concrete masonry. The factors that are known to affect the strength of this type of masonry are discussed with the varying results and interpretations highlighted. There is consensus that increasing axial stress increases the shear strength and reduces the ductility of the masonry. However, whether reinforcement (both horizontal and vertical) contributes to strength remains an issue of debate, as is the effect of aspect ratio. Most codes and standards do not differentiate fully grouted from partially grouted masonry, often over predicting the shear strength of the latter. Wall versus panel failure is not considered. Much work needs to be done to improve our understanding of this material subject to in-plane shear.