Changes in Asian monsoon variability can affect more than 50% of the world population, yet our understanding of the monsoon is incomplete. The proposed research will bring new insight into this crucial component of the Earth’s climate system while using world-class equipment and resources available at the host institution, the University of Oxford. This research will contribute to a deeper understanding of a critical but understudied portion of the Asian monsoon, the Southeast Asian monsoon, by producing a high-quality climate reconstruction using speleothems (cave carbonate formations) from Laos. Speleothems are widely considered as one of the best climate archives available. They can be precisely dated and their geochemical composition preserves long and detailed information of past climate change. I will capitalize on these properties of speleothems to address key questions regarding past variability of the Southeast Asian monsoon: (1) What is the long-term history of the Southeast Asian monsoon, and how does this compare to records from the South and East Asian monsoons? (2) Are recent changes in the relationship between El Nino and the monsoon a response to global warming? (3) Are changes in Southeast Asian monsoon strength driven from the northern or southern hemisphere? (4) Can comparison of oxygen isotope records along moisture transport pathways provide quantification of past rainfall? The societal and economic implications of climate change ensure that understanding the behavior of the climate system will continue to attract widespread research, together with public, economic, and government interest, for decades to come. Moreover, an understanding of the mechanisms of climate change that impact the Asian monsoon region, as proposed here, is essential for scientists and policy makers in the European Union and worldwide because climate variations are known to influence key natural resources and are associated with regional hazards and disasters.