This publication is part of ongoing work within the OECD’s Directorate for Agriculture on the structural and behavioural changes in the agro-food system. Agri-food supply chains have undergone important structural changes since the 1990s that have altered the way firms do business. One of the most striking changes is the ongoing rise in the scale of operations of food firms at all points along the supply chain, most notably in food retailing. The rise of retail concentration has led to the concern that retailers may abuse their market power vis-à-vis other actors with smaller market shares, in particular farmers and consumers. This study addresses this concern in two ways. First, it describes recent changes in retail concentration and the related changes in retail buying behaviour. Second, it shows, in an illustrative way, how one can possibly pursue empirical analysis of whether retail buying and selling behaviour disadvantages both suppliers, among which are farmers, and consumers.