Hydrometry observes the components of the hydrological cycle such as rainfall, groundwater characteristics and water quality. It also studies the flow characteristics of surface waters. It is concerned with the measurement of the components of the hydrological cycle, such as the quantification of water resources. Hydrometry encompasses concepts from various areas of engineering such as hydrology, control systems, computer sciences, data management, and communications. It uses the hydrometer to measure the characteristics such as density and specific gravity of a liquid. Hydrometry is primarily concerned with measuring the river flows. These measurements are useful in predicting and managing the river flows that can control floods. It also helps in water supply, agriculture and energy production. This book discusses the fundamentals as well as modern approaches to hydrometry. It presents researches and studies performed by experts across the globe. It will serve as a valuable source of reference for graduate and post-graduation students.