In this paper, we put forward the notion of “energy sovereignty from below” to reflect on the visions and practices of territorial movements mobilizing around corporate energy projects and for reclaiming control over the definition, modalities, and scales of a just socioecological transition. Based on a comparative engagement with the cases of Puerto Rico and Catalonia, first, we explore how movements organize to challenge the undesired impacts of energy projects, paying specific attention to how their struggles are grounded in the defense of land/territory and in claims against multiple forms of colonialism and extractivism. Second, we examine their energy self-provision initiatives, including community-owned renewable energy projects—as concrete manifestations of energy sovereignty from below—to understand how and to what extent these contribute to empower movements, create solidarities, and provide prefigurative alternatives to corporate-controlled transitions. Comparing these two cases provides opportunities for a South/North dialogue around the meaning of energy sovereignty, the commonalities and differences in conditions and priorities for struggles, and the complexities of applying a framework of “energy colonialism/sovereignty” in global North countries.