The water cycle is the continuous movement of water above, below and on the Earth's surface. The mass of water on Earth remains constant but it differs in its distribution among the reservoirs of ice, saline water, freshwater and atmospheric water. The variation in the amount of water present in various reservoirs depends on the climatic variables. Several physical processes such as evaporation, condensation, infiltration and precipitation move water from one reservoir to another. The water takes different forms such as solid, liquid and vapor while going through such processes. The water cycle is driven by the sun that heats water in oceans and seas and makes it evaporate as water vapor into the air. Sometimes ice and snow sublimate into water vapor. These water vapor move across the globe and form clouds, which collide and fall out on the upper atmospheric layers as precipitation. Most water comes back into the oceans, seas and on land as rain. This book outlines the processes and applications of water cycle in detail. It includes some of the vital pieces of work being conducted across the world, on various topics related to the water cycle. This book is a collective contribution of renowned group of international experts.