The Caspian Sea’s water levels are declining. While the science of Caspian Sea fluctuations is complex, there is growing evidence that substantial further declines will occur in the next 50 years, with impacts on the environment, economies, infrastructure and sustainable development. Coordinated, scientific research is required across and beyond the Caspian Sea littoral states to address the relationships between changing temperatures, winds, evaporation, precipitation, discharge from rivers, human water use and diversions. Climate change is influencing all these variables and hence joint analysis of climate and adaptation science will also help Caspian states to understand the challenges, identify appropriate adaptation options and plan effectively for the future.