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.