This chapter describes solar azo-switches that undergo effective E → Z photoisomerization by sunlight. Azo molecules that can undergo E → Z photoisomerization are the most widely studied photoswitches, which are used for the development of photoresponsive systems and the storage/conversion of light energy. One general feature of azo-switches is that they need to be activated by narrow-band light for effective photoconversion, which limits their ability to directly work under sunlight and to efficiently harvest solar energy. In this chapter, we introduce sunlight activated azo-switches with E → Z photoisomerization yields exceeding 80% under unfiltered sunlight. These sunlight-driven azo-switches are developed by rendering the absorption of E isomers overwhelmingly stronger than that of Z isomers across a broad ultraviolet to visible spectrum. A simple yet tunable molecular design strategy is established to meet this spectral requirement, enabling the extension of the light absorption beyond 600 nm. Moreover, the half-lives of Z isomers are tuned from days to years at room temperature and Z → E photoconversion can be achieved without impairing the forward solar isomerization. Such solar azo-switches provides unprecedented opportunities for developing sustainable light-driven systems and efficient solar energy technologies.