Water is one of the most important factors for the development of woody tree crops and vines, and its scarcity is considered a major source of stress. Water deficit severely affects plant yield because it reduces photosynthetic capacity, which is reflected in lower accumulation of the carbon dioxide required for vegetative growth and fruit size. Regulated deficit irrigation (RDI) is a common irrigation strategy based on water restrictions applied in non-critical phenological periods, when fruit growth is less sensitive to soil water deficits, while during the rest of the season the full water requirements of the trees are met. The present study reviews the different effects of water deficit on plant yield and water relations, including the tolerance of different water deficit levels, ranging from mild to extreme. The results obtained concerning the benefits of different RDI strategies are compared.