The monograph is devoted to the study of water runoff of rivers of Ukraine under climate change conditions. It consists of 5 chapters, which describe different approaches to the study of water runoff and forecasting its changes. Elements of the hydrological regime of rivers, such as the normal water runoff, maximum and minimum runoff, intra-annual runoff distribution and regulation of water runoff of rivers in Ukraine are analyzed. Methodical approaches to construction of the map of water runoff specific discharge of the rivers of Ukraine. The analysis of long-term fluctuations of river water runoff is performed according to the observations, the time fluctuations of average, maximum and minimum runoff are considered based on the analysis of difference integral curves. Methodical approaches to changes in the average long-term water runoff of rivers based on stochastic patterns, water balance modelling and climate projections for the XXI century are presented.