Governments across the world are coming under increasing pressure to invest heavily in projects that have maturities of decades or even centuries. Key areas of concern include climate change mitigation, environmental and biodiversity protection, nuclear decommissioning, enhancing infrastructure and coastal defenses, and long-term health care management. Whether such projects are evaluated as being economically justifiable depends on the social discount rate (SDR) that the government deploys. This variable converts the future costs and benefits of public policy into their value today, thereby facilitating the comparison of social investments with different maturities. Critically, the result of such analysis is extremely sensitive to small changes in the choice of the SDR, yet policy guidelines differ widely across countries and international institutions. In this article, we provide a review of the academic literature on long-term SDRs, with particular emphasis on how these insights have been integrated into governmental guidance.