Water cycle or hydrological cycle refers to the continuous circulation and movement of water on the surface of earth and in the atmosphere. Water cycle involves major reservoirs of ice, saline water, fresh water and atmospheric water. The mass of water in the biosphere remains constant as the water moves from one reservoir to another. It involves processes such as evaporation, condensation and precipitation. The water cycle involves energy consumption which can result in alteration of temperature. It is essential and crucial for the maintenance of ecosystem and life on the earth. Human activities like agriculture, industrialization, pollution, deforestation and construction of dams has altered the balance of the water cycle which has resulted in glacial retreat, global climate change, loss of water resources and global warming. This book outlines the processes of water cycle in detail. It unfolds the innovative aspects of water cycle and hydrology which will be crucial for the progress of this field in the future. A number of latest researches have been included herein to keep the readers up-to-date with the global concepts in this area of study.