Facing the world's ecological, economic, and social challenges requires us to connect the concepts of justice, sustainability, and transitions. Bridging and discussing heterogeneous fields, we argue that these concepts need to complement each other, and we present just sustainability transitions (JUSTRAs) to do so. To define JUSTRAs, we review the state-of-the-art literature, focusing on the understanding of these three concepts and their pairings in various disciplinary fields and empirical settings (e.g., environmental justice, just transitions, sustainability transitions, energy justice, food justice, urban justice). We center marginalized voices to highlight the processes of radical transformative change that JUSTRAs seek. We offer three analytical lenses that further the understanding of JUSTRAs: politics, power, and prefiguration. We argue that these complementary lenses are necessary to remake the world in both critical and pragmatic ways. Finally, we present a research agenda on JUSTRAs, foregrounding three complementary modes of inquiry: analyzing, critiquing, designing.