Water stress is intensifying under climate change, demographic growth, and socio-political pressures, raising urgent questions about how shared waters are governed. This article has a dual aim: to take stock of scholarship on water, conflict, and cooperation, and to frame the contributions of this Special Issue on “Water, Environment, and Security.” We combine a bibliometric mapping (2010–2024) with a thematic synthesis to trace field-level trends and recurring debates. The review highlights seven focal areas: power and hydro-hegemony; river-basin organizations; climate change framing on compound risks; environmental peacebuilding across scales; technological innovations; justice and equity; and the targeting of water in war. We show that conflict and cooperation frequently coexist and are mediated less by hydrology than by institutions, power relations, and inclusion. As a whole, the Special Issue advances this research agenda through diverse epistemologies and methods, conceptual frameworks, comparative and ethnographic studies, and large-N analyses, linking outcomes from households to basins. Looking ahead, we outline research frontiers in water research, including open hydrology data, justice-centered governance, war impacts, and translating transboundary commitments into local practice. Together, these insights point to pathways for more equitable, resilient cooperation over shared waters.