This Special Issue of Annals of Botany presents research on plant responses to water stress, covering molecular, physiological, and agronomic aspects. Recent advances in genomics have enabled a deeper understanding of gene expression and signaling pathways related to water deficits. Microarray technology helps identify genes affected by stress, improving understanding of cell- and tissue-specific responses. The issue also examines the effects of water deficits on Rubisco, photosynthesis, and photorespiration, highlighting the role of abscisic acid and the importance of antioxidant systems. A major topic is the distinction between stomatal and non-stomatal inhibition of photosynthesis. Controversy exists regarding the extent to which photosynthesis recovers under elevated CO₂ during water stress. Studies suggest that both stomatal and non-stomatal effects contribute, depending on the severity of the deficit. The midday depression of photosynthesis in Quercus suber is attributed to stomatal closure and reduced Rubisco activity. The issue also discusses how these responses translate to field conditions, with implications for crop selection and yield. Genotypic variations in stress response are considered, particularly in wheat and sugar beet. The integration of physiological and genetic markers is essential for future research. The Special Issue reflects the discussions at a symposium on plant responses to water stress, emphasizing the importance of photosynthetic, metabolic, and molecular responses in crop yield selection. The papers highlight the need for further research to resolve the debate on stomatal vs. non-stomatal effects and to improve understanding of plant responses to water stress.This Special Issue of Annals of Botany presents research on plant responses to water stress, covering molecular, physiological, and agronomic aspects. Recent advances in genomics have enabled a deeper understanding of gene expression and signaling pathways related to water deficits. Microarray technology helps identify genes affected by stress, improving understanding of cell- and tissue-specific responses. The issue also examines the effects of water deficits on Rubisco, photosynthesis, and photorespiration, highlighting the role of abscisic acid and the importance of antioxidant systems. A major topic is the distinction between stomatal and non-stomatal inhibition of photosynthesis. Controversy exists regarding the extent to which photosynthesis recovers under elevated CO₂ during water stress. Studies suggest that both stomatal and non-stomatal effects contribute, depending on the severity of the deficit. The midday depression of photosynthesis in Quercus suber is attributed to stomatal closure and reduced Rubisco activity. The issue also discusses how these responses translate to field conditions, with implications for crop selection and yield. Genotypic variations in stress response are considered, particularly in wheat and sugar beet. The integration of physiological and genetic markers is essential for future research. The Special Issue reflects the discussions at a symposium on plant responses to water stress, emphasizing the importance of photosynthetic, metabolic, and molecular responses in crop yield selection. The papers highlight the need for further research to resolve the debate on stomatal vs. non-stomatal effects and to improve understanding of plant responses to water stress.