Many terrestrial ecosystems are limited by drought and predicted increases in the frequency and intensity of droughts associated with climate change likely will lead to increased plant mortality in the future. The central role that water plays in life on earth has led to a rapid increase in interest in understanding the causes of vegetation drought mortality, with implications for managing water resources sustainably. Currently, theoretical and field-based ecologists are pursuing research projects in ecohydrology, plant ecophysiology, landscape ecology and other fields in a diverse range of ecosystems. Two mechanisms, carbon starvation and hydraulic failure, have been proposed as the primary drivers of drought mortality, with biotic factors such as pests and disease also playing a role. The relative roles of these mechanisms, however, and the underlying morphological and physiological processes through which they interact, remain unclear. For this session, we have invited speakers who will provide talks designed to span the current state of knowledge in this field, and identify the critical next steps to address gaps in our knowledge. This session is clearly linked with the sessions organized by Henry Adams, “Ecological consequences of climate- and infestation-caused tree mortality, from populations and communities to climate change and earth system feedbacks” and by Erin Wiley, “Carbon or Sinks: The Causes of Tree Growth Limitation". The speakers include theorists and field scientists, representing a range of perspectives and ecosystem types. Leading international researchers will provide syntheses on key learnings and outstanding questions for mechanisms leading to drought mortality, and unresolved issues which need to be considered. Speakers will discuss whether carbon starvation and hydraulic failure can be mechanistically linked, using a modeling approach, and describe results from one of the few broad-leaved experiments, discussing hydraulic changes which occur with mortality in clonal Aspen forests. We will conclude the organizer synthesizing the previous speakers findings. Finally, we propose to have an informal discussion workshop following the presentations to meet with other like-minded researchers to discuss and prepare a manuscript which synthesizes findings, themes, uncertainties, and research gaps.