Plant adaptation to global climate change has become one of the most pressing and important topics in biology. Changes in climate that lead to increased crop water use or decreases in water availability will increase the frequency and magnitude of plant water stress. Water stress reduces plant growth and crop yield, and for perennial crops like grape, there is an added con- sideration: their long-term ability to tolerate and recover from this stress. This primer introduc- es plant water relations basics, explaining how grape physiology is affected by water stress and discussing the physiological foundations for the development of drought-tolerant cultivars and rootstocks.