Droughts have been predicted to increase in frequency and intensity over Amazonia in the future (Joetzjer et al. 2013; Boisier et al. 2015) and the vulnerability of Amazonian ecosystems to such extreme events have already been observed (Phillips et al. 2009; Lewis et al. 2011). Understanding and predicting the responses of such hyper-diverse communities thus constitutes a critical research challenge. Yet, precise information on large sets of tropical forest species (tree, lianas, epiphytes) is still lacking and simulation by models usually rely on characteristics of a very limited amount of species gathered in published papers. In DROUGHT, we want to improve our knowledge on plant interspecific variability in resistance to drought and on the way models simulate tropical forest ecosystem responses to drought. We will combine a series of observational and experimental approaches in order to (i) evaluate the strategies of large sets of tropical trees, lianas and epiphytes to cope with drought (physiological or morphological mechanisms of avoidance or tolerance), (ii) identify trade-offs among functional strategies, (iii) identify the role of biotic factors, including mycorrhizae and endophytes involved in drought avoidance/tolerance strategies, (iv) evaluate drought impact on tropical ecosystem functions, (v) understand drought response patterns at community and ecosystem scale. Through our research on the vulnerability of tropical plants and ecosystems to drought, we will help providing predictions of future biodiversity and ecosystem functioning under future climatic regimes. Results from DROUGHT will thus not only allow publishing scientific papers, but they will also contribute predicting the future role of these ecosystems in the global carbon balance. DROUGHT relies on new data that will be obtained through (i) field campaigns in French Guiana or at other sites around the tropics (Panama, and Caxiuana site in Brazil), (ii) botanical garden collections, (iii) in situ drought experiments (on epiphytes or tree saplings: common garden experiments), or (iv) greenhouse experiments. Furthermore, DROUGHT will make use of recently measured data, such as tree growth, mycorrhizae observations, leaf or wood functional traits, ecosystem level fluxes ? collected during recent CEBA or non-CEBA projects in French Guiana or other projects led by non-CEBA partners. The proposed research addresses some of the most important objectives of Labex CEBA by studying the functional diversity of tropical plants (trees, lianas, epiphytes) (WP2) and interactions among species (plants, mycorrhizae, endophytes) (WP4). It will contribute to improve the links between biodiversity and ecosystem processes through the development of modelling concepts and parameterisations of models in collaboration with modellers, particularly those from the CEBA-METIST strategic project. Furthermore, it will contribute to the Educational issues of CEBA, through the possibilities of training periods offered to M1 and M2 students and seminars/conferences given by CEBA or non-CEBA partners when they will visit French Guiana.