Plants are generally exposed by many environmental (both biotic and abiotic) stresses. Among the environmental stresses, drought is one of the most important abiotic stresses in plants, which affects crop growth and development. Drought is a meteorological term and is commonly considered as a long period without significant rainfall. On the base of harshness and time-period, drought tolerance is seen in almost all plant species, but its extent varies from species to species and even within species. In this book, the drought stress tolerance in plants has been discussed in detail. The main purpose of the book is to let the students understand basic concepts of drought stress in plants. The book has been designed in such a way that it is not only useful for the students but equally useful for practicing Bioenergetics and researchers in field of Botany.