Hydropower (HP) generation is significant for energy supply especially in the climate convenient regions of the world, where there are frequent storm rainfall that provides support for surface flow, which is the main source of hydroelectric power (HEP) production. The fundamentals and systems of HP are presented based on historical, climatic, hydrologic, engineering, and technological points of view. There are four different systems for HP generation, which are impoundment, diversion, pumped storage and other types that are extractable from tides, waves, heat, and current flows. Each one of these alternatives is explained in detail by taking into consideration climate, environment, hydrology, sustainability, and strategies with case studies. Although there are different methodologies and technologies for HP energy generation, this chapter provides the fundamental of such implementations and provides a general …