The global water cycle or hydrological cycle is a fundamental Earth system process that governs the continuous circulation of water through the atmosphere, lithosphere, hydrosphere and biosphere. Driven primarily by solar energy and gravity, it integrates physical, chemical and biological processes, thereby regulating climate, sustaining ecosystems and ensuring the availability of freshwater for human societies. Key fluxes such as evaporation, transpiration, condensation, precipitation, infiltration and groundwater flow, which connect terrestrial, aquatic and atmospheric systems across diverse spatial and temporal scales. The water cycle reinforces global energy balance through latent heat exchanges, influences albedo through cloud and ice cover and sustains biogeochemical cycles by transporting nutrients and carbon. However, this vital system is increasingly disrupted by anthropogenic pressures. Climate change is intensifying extremes of drought and flooding, altering precipitation regimes and accelerating glacier and snowpack retreat. Land use changes, such as deforestation, urbanization and agriculture, further destabilize evapotranspiration and runoff patterns, while groundwater overextraction and pollution threaten long-term water security. These pressures compound risks to biodiversity, ecosystem functioning and human livelihoods, particularly in vulnerable regions already facing water scarcity. This chapter examines the structure, dynamics and functions of the global water cycle, while highlighting the growing challenges posed by anthropogenic influences. It emphasizes the need for integrated and adaptive strategies ranging from advanced monitoring technologies to nature-based solutions and transboundary governance to ensure sustainable management of freshwater resources and enhance resilience in a rapidly changing world.