High levels of corporate concentration and power in agrifood supply chains raise important policy concerns because they can affect food systems in adverse ways. In this paper, we argue that increased corporate concentration and power in food systems has the capacity to undermine people’s agency– that is, their capability to make choices and exercise their voice. We explore three dimensions of the relationship between concentrated corporate power and people’s agency in food systems. First, dominant firms within highly concentrated food system segments can exercise market power, which enables them to earn excess profits – often by charging higher prices, suppressing wages, and weakening livelihood opportunities. Second, dominant agrifood firms have the capacity to shape material conditions within food systems – determining prevailing technologies used in food production, working conditions, levels of processing of packaged food items, and food environments – in ways that can affect people’s choices. Third, dominant agrifood firms can exercise political power by actively pursuing strategies to influence food policy and governance processes via lobbying and other more indirect measures, weakening opportunities for broader democratic participation in food systems governance. Given these potential outcomes, more policy attention should be paid to corporate concentration and its implications for agency within food systems.