Heterojunctions have interesting optical properties which make them attractive for solar cells. Several types of heterostructure solar cells have been investigated: heteroface, abrupt heterojunction, and graded‐gap heterojunction solar cells. The primary advantage of heterostructure cells is the enhanced short‐wavelength response although there is potential for low‐cost cells with polycrystalline material. The improvement in solar‐cell performance for heterojunctions depends upon the selection of semiconductors with useful energy gaps that are closely matched in lattice‐spacing and thermal‐expansion coefficients. The importance of the heterojunction interface and its dependence on material properties is discussed. Various fabrication methods are discussed and their application to the different types of heterostructures. Recent performance data for material systems representative of each type of heterostructure cell are discussed and considered in terms of maximum expected performance.