This chapter deals with the design of penstocks. Water is carried from the surge tank or forebay to the water house in a closed conduct. When it is laid on natural ground surface it is called penstock. When it is laid inside the rock mass, it is called pressure shaft. These are generally steel pipes. The layout, number and size of penstocks are described along with the structural design of the shell subjected to different loads. The penstock which is laid on the surface needs supports, anchors at the bends and the expansion joints for temperature variation. The design features and procedures for designing these structures are also described in this chapter. The design of pressure shaft is also briefly described. The pressure shafts are rarely used in SHPs.