Climate change adaptation in water management is a water governance issue. While neither climate change nor water respects national borders, adaptation in water management should be treated as a transboundary water governance issue. However, transboundary water management is, in essence, more complex than national water management because the water management regimes usually differ more between countries than within countries. This paper provides 63 lessons learned from almost a decade of cooperation on transboundary climate adaptation in water management under the UNECE Water Convention and puts these into the context of the OECD principles on water governance. It highlights that good water governance entails a variety of activities that are intertwined and cannot be considered stand-alone elements. The paper also shows that this wide variety of actions is needed to develop a climate change adaptation strategy in water management. Each of the lessons learned can be considered concrete actions connected to one or more of the OECD principles, where a range of actions may be needed to fulfil one principle. The paper concludes that developing climate change adaptation measures needs to improve in parallel the water governance system at transboundary scale.