This article, which is part of the North–South Legal Mapping Project, considers land law and land use in each jurisdiction on the island of Ireland. The first part provides a sketch of the basic structures of land law, identifying a remarkable level of convergence (or, more accurately, absence of divergence), which is only partially qualified by recent comprehensive land law reform in Ireland, notwithstanding the absence of comparable reforms in Northern Ireland. The second part considers land use, where there is greater (and increasing) potential for divergence, particularly in environmental governance. The article sketches and explains core influencing factors that have shaped the evolution of environmental governance on the island to date, before considering how Brexit and subsequent developments impact regulatory alignment across the island. It focuses on the issue of water protection and river basin management, in light of the three transboundary river basins on the island.