Abstract The pursuit of civil nuclear power, frequently justified in the name of national energy security, paradoxically entangles most states in long-term interdependencies with the few countries that can supply nuclear technologies. These interdependencies are insufficiently documented and poorly understood. This article presents and analyzes a new dataset of nuclear cooperation agreements signed or announced between 2000 and 2015. We find that Russia and the US dominate international technological nuclear cooperation, with the US’ dominance particularly prominent in safety and security and Russia's in nuclear power plant construction, reactor and fuel supply, decommissioning and waste. When it comes to these technologies, Russia is the supplier in approximately half of all agreements; France, the US, China, Korea, and Japan together account for another 40%. All in all, six countries are suppliers in over 90% of all international nuclear agreements, a far higher supplier concentration than in oil and gas markets. These results show that the global future of nuclear power depends as much on international cooperation as on national motivations and capacities. Effective policies and institutions supporting the safe use of nuclear power should therefore be directed at managing its international as well as national aspects.