While the popularity of transition approaches to transform agriculture and food systems has surged, evidence that these approaches serve rather than change the dominant institutional order, and thereby do little to address underlying causes of unsustainability, is mounting. This thesis investigates the different way in which social movements foster transformation by looking at the agroecology movement in Brazil. By combining insights from affect theory, political economy and political discourse theory it captures how the agroecology movement challenges the dominant order and advances alternatives in the domains of practice, territory and the wider institutional environment. The thesis shows that affects play a central role in mobilising people and building alternative, more caring ways of production, distribution and life. It also shows how the agroecology movement combines diverse forms of resistance and politics to support and protect alternatives from hostile forces and co-optation by powerful agents, while building a broad, popular movement. The thesis concludes that in contrast to transition approaches, social movements have the potential to foster transformation that is bottom-up, equitable and democratic.