Water deficit (drought) is one of the main abiotic constraints to the yield of cereal crops worldwide though the impact is intense in tropics and sub tropics. It has gaining important attention because of climate change which has been affecting the intensity and distribution of rainfall. The author attempted to investigate the impact of water stress imposed during various developmental phases on physiological performances of tef (Eragrostis tef). The first section of the book provides conceptual background on impact of water stress on crop productivity. The second section is devoted to theoretical framework. The third section is concerned with methodological approaches to conduct water deficit experiments. The fourth and fifth sections presented the main theme of the book. As there are very little academic literatures exists on this subject, this book, therefore provides vital knowledge to researchers, students and anybody interested to know tef, an endemic Ethiopian cereal crop. The book should offer especial benefit for tef breaders to incorporate physiological traits in their attempt to improve its drought resistance.