This article theorizes the politics of responsibility—activist struggles over who will be held accountable for structural injustices like the “catastrophic” changes underway in our climate. To do so, it develops a politicized conception of responsibility, one that treats responsibility as a social construct and a terrain of contestation. Building on the work of feminist philosophers of responsibility and on the praxis of “kayaktivism,” this politicized account treats responsibility as a social practice of interrogating and contesting shared ethico-political judgments. On this understanding, taking responsibility or stepping up is a way of making responsibility—literally of (re)constructing those social practices and judgments through conscious efforts to persuade others, challenge prevailing norms and interpretations, change people’s beliefs about how the world works, revise popular expectations of social actors and institutions, and disrupt business as usual. The article highlights the centrality of norms and power to social practices of responsibility and suggests alternative perspectives on familiar philosophical worries about blame, complexity and agency, and justification.