The Anthropocene requires remaking social structures and practices. Who can do this, giving form and meaning to values such as justice, democracy, sustainability, and conservation, thereby disrupting path dependencies in ideas? Discourse entrepreneurs are leaders and activists who can advance discourses such as that of the Anthropocene itself, or shift the balance within or across discourses (such as moral and religious ones) in an ecological direction. Other vital agents include scientists and experts, cities and sub-national governments, and those most vulnerable to a damaged Earth system. Non-human nature can play a role. More conventional agents such as states, international organizations, and corporations, whose actions are vitally important receive less attention because they are not well placed to initiate change in ideas. Using illustrations from biodiversity, climate governance, and elsewhere, this chapter shows how formative agency can transform the meanings and principles that guide institutions and practices, through argument, rhetoric, and deliberation.