This book describes some key global water challenges, perspectives for remote sensing approaches, and their importance for water resources-related activities. It presents eight key types of water resources management variables, a list of sensors that can produce such information, and a description of existing data products with examples. This book provides a series of practical guidelines that can be used by project leaders to decide whether remote sensing may be useful for the problem at hand and suitable data sources to consider if so. The book concludes with a review of the literature on reliability statistics of remote-sensed estimations.