Silicon heterojunction solar cells are crystalline silicon-based devices in which thin amorphous silicon layers deposited on the wafer surfaces serve as passivated, carrier-selective contacts. The success of this technology is attributable to the ability of amorphous silicon to passivate dangling bonds—thereby removing surface recombination sites—without blocking charge carrier transport. This unique combination allows the recombination-active metal contacts to be displaced from the wafer surfaces, enabling record-high open-circuit voltages of up to 750 mV and efficiencies of up to 25.6%. This chapter introduces the silicon heterojunction concept and discusses device fabrication, operation, and manufacturing. Active areas of research and likely future developments are identified throughout.