It is over a century ago that testing of reinforced concrete slabs by the pioneers of the material such as Lord, Turner and Maillart showed that restrained slabs could carry significant loads. Since that time the interest in and knowledge of the internal arching, or compressive membrane action, that enhances the strength of reinforced concrete has waxed and waned. In this paper, definitions of key terms such as arching action, compressive membrane action and geometric arching are given. A review of key twentieth century research and testing is also given, with particular emphasis on aspects related to bridge decks. The more recent advances in compressive membrane action and punching shear are then outlined. A graphical summary of key tests is presented, together with an initial analysis of these data. The current American, British and European bridge codes incorporating compressive membrane action are reviewed and the major differences outlined in the light of this recent research. Finally the key issues are summarised and a few thoughts on future research and the codification of arching action and compressive membrane action are given