This chapter delves into the role of power in sustainability transitions, addressing the limited attention power dynamics have received in the field despite their centrality to lasting societal change. Drawing on theories of power from various disciplines, this chapter introduces two conceptual frameworks to analyse power: (1) ‘power to, over, and with’, which examines how and which power relations change over time, and (2) ‘three relations of power, which focuses on how power relations are constituted and shape societal change. These frameworks are applied to a case study of community-supported agriculture (CSA) in Portugal, showcasing grassroots efforts to address socio-political and ecological challenges while striving for sustainable agri-food systems. The analysis reveals how power influences opportunities and barriers for transitions, emphasising the interplay between individual and collective agency, human and non-human interactions, and historical structures of social relationships. The chapter concludes by emphasising the need for more power-aware research that integrates diverse perspectives, including non-Western and Indigenous epistemologies, to deepen the understanding of power in sustainability transitions.