In this article we review the current state of the field of solar neutrinos, including flavor oscillations, nonstandard effects, solar models, cross section measurements, and the broad experimental program thus motivated and enabled. We describe the historical discoveries that contributed to current knowledge, and define critical open questions to be addressed in the next decade. We discuss standard solar models, including uncertainties and problems related to the solar composition, and review experimental and model solar neutrino fluxes, including future prospects. We review the state of the art of the nuclear reaction data relevant for solar fusion in the proton–proton chain and carbon–nitrogen–oxygen cycle. Finally, we review the current and future experimental programs that can address outstanding questions in this field.