The hydrologic cycle is described. The mechanisms of erosion due to hydraulic action are discussed. A summary of conventional erosion control techniques and systems is provided. This includes the use of vegetation and timber products; rocks and stones; and concrete unit products. The functions of geosynthetic erosion control products may be summarized as ground cover, turf reinforcement, material confinement and material containment. In ground cover, the product minimizes the impact of rain droplets and prevent the detachment of soil particles. In turf reinforcement, the product improves the erosion resistance of vegetation. In material confinement, the product enhances erosion resistance of the soil that they help confine. In material containment, the product when filled with the selected material becomes a structural unit to replace of rock or concrete units to resist the forces of erosion, thereby protecting the base soil below. The application and design of geosynthetics for erosion control in hydraulic environment are presented. Several case studies are described.