Hydroborates represent a promising, yet underexplored, class of electrolytes for all-solid-state batteries. This article reviews the rapid recent developments that enabled the demonstration of first all-solid-state batteries based on hydroborate electrolytes with remarkable cycling stability. High-ionic conductivity, a wide electrochemical stability window, and advantageous mechanical properties make hydroborate electrolytes serious candidates for addressing the major device integration and processing challenges faced by all-solid-state batteries. We also discuss novel approaches for the synthesis of hydroborate compounds from cost-effective feedstock chemicals with low toxicity. Finally, we provide an up-to-date assessment of the key performance metrics of hydroborate electrolytes in comparison to other more established solid electrolyte materials and discuss future research opportunities in the field.