To date, very few studies have assessed the impact of summer droughts on forest biodiversity and ecosystem functioning. Decreased ecosystem productivity and increased mortality are general consequences of drought on biodiversity. Competitive species, species adapted to cold and wet conditions as well as species with low reproduction rates and/or limited mobility seem the more affected. However, species-specific effects are regulated by mechanisms allowing for resistance to drought. The short-term consequences of drought on biodiversity depend on species abilities to resist, and to recover after, drought, and on competitive interactions between species. Although the abundance of many species generally decreases during drought, some taxa may increase in number during drought or shortly after. The effects of recurrent droughts must be evaluated in the wider context of global climate and habitat change. Considering the predicted increase in drought frequency and intensity, interdisciplinary research initiatives on this issue are needed urgently.