With over half of US states adopting renewable energy goals, and countries across the world setting ambitious renewable targets, the need for long-duration bulk storage is becoming pressing as evidenced by ever-increasing amounts of curtailed renewable electricity. Matching abundant, low-cost, renewable generation supply with demand throughout the year requires longer-duration storage, including multi-day and seasonal storage. Without significant deployment of long-duration storage, clean energy policy goals will not be met. What technologies will play the greatest role in providing long-duration storage? How can we best value the reliability provided by long-duration storage?