Around the world, underground reservoirs have been successfully used for secure and long-term storage of gas. The first instance of natural gas storage underground occurred in 1915, where a depleted natural gas well was repurposed into a storage field in Ontario, Canada. While the first instance of carbon dioxide storage underground was in the early 1970s, where associated storage of carbon dioxide was a result of enhanced oil recovery operations in the United States. These forms of gas storage continue to play a vital role in meeting our goals for energy security, affordability and sustainability. Over the years, the behaviour of stored gas in the subsurface has become well understood and documented by both engineers and geologists. Furthermore, fit-for-purpose techniques for drilling, completion and ongoing monitoring have advanced dramatically – in particular in recent years due to the rise in carbon capture, utilization and storage projects (CCUS) globally. Underground storage reservoirs now face their next test – hydrogen. As the development of the hydrogen industry continues, it is becoming increasingly clear that the use of underground reservoirs will be critical to ensure safe and secure storage of hydrogen in large quantities. In a future where excess renewable energy is converted to hydrogen, underground reservoirs provide a long-term storage solution that can balance energy systems or be used as a buffer for direct hydrogen use. While the storage of hydrogen underground presents its own unique technical challenges in the subsurface, there is still much that can be gleaned from past and current experience in gas storage including CCUS. This special session aims to discuss those experiences and how they may help propel forward the technical readiness of underground hydrogen storage worldwide.