Cs2AgBiBr6, as a benchmark lead‐free double perovskite, has emerged as a promising alternative to lead‐based perovskites because of its high stability, non‐toxicity, exceptional optoelectronic properties, and multifunctionality. To encourage further research on Cs2AgBiBr6 and its broad applications, in this review, its fundamental properties including the structure‐property relation, synthesis, stability, origin of absorption and photoluminescence, electron‐phonon coupling, role of defects, charge carrier dynamics, and bandgap modulation are comprehensively emphasized. The recent progress on the wide applications including solar cells, light/X‐ray detectors, and ferroelectric/magnetic devices are highlighted. Moreover, the challenges of Cs2AgBiBr6 materials and related applications are discussed and perspectives are provided for guiding the future development of this research area. [ABSTRACT FROM AUTHOR]