This paper analyzes the principled content of 62 international river agreements for the period 1980-2000. We ask two questions: whether governments are converging on common principles for governing shared river basins and whether the effort to create a global normative framework for shared rivers has shaped the principled content of basinlevel international accords. The data reveal a complex process of normative development. A few core principles emanating from global legal efforts have shown significant growth, diffusion and deepening at the basin-specific level. Others are common in basin agreements but show no diffusion or deepening. Still others are weakly represented in the data. If joint articulation of common principles is necessary for regime formation, then there is only weak evidence for a global rivers regime. But the data also reveal normative developments not captured by a regime-theoretic lens: a backlash reinforcing sovereign rights, the emergence of two seemingly conflicting clusters of principles, and an ambiguous relationship between some principles typically thought to be mutually reinforcing. The results show the need to treat principled content as an important dependent variable in the study of cooperation and to view institution building as a dynamic, multi-dimensional and multi-level process.The world's major rivers create complex challenges of international cooperation. There are an estimated 263 internationally shared rivers ) flowing through basins that cover some 45% of the Earth's land surface. One hundred and forty-five countriesFall but a handful of the world's nonisland statesFhave some portion of their territory in an international basin. Of these, almost two-thirds have at least half of their national territory lying in an international basin.