In the last two decades the human population of the world has increased, thus necessitating an increase in crop production, which demands increasing amounts of water and minerals, which in many parts of the world where population increase is greatest, are in short supply. Water is the most important factor limiting crop yield. Every aspect of plant physiology and plant growth is affected by water directly or indirectly. Uptake of water by plants is mostly via the roots. It is widely recognized that most plant roots growing in natural environments develop symbiotic associations with mycorrhizal fungi. This book provides an overview of the specific mycorrhizal fungi which has a consistent beneficial effects on plant growth, mineral uptake, CO2 exchange rate, water use efficiency, transpiration, stomatal conductance, photosynthetic phosphorus use efficiency and proline accumulation under well-watered and drought stressed conditions .