This chapter focuses on penstocks of hydropower station. Firstly, functions and types of penstocks are introduced, and water supply modes and hydraulic calculation are briefly described. Then, materials and strength of steel penstocks are elaborated, facilities and structure are introduced, and design loads and load combinations of penstocks are listed. For exposed steel penstocks and other types of penstocks, including underground penstocks as well as dam body penstocks and penstocks laid on the downstream surface of dams, their respective characteristics and layout are introduced. Structural analysis as well as the stability against external pressure is carried out in details with assumptions and equations.