Hydrogen has become increasingly popular as one of the alternative fuels to reduce greenhouse gas emissions. Storing hydrogen in geological structures is a technology that shows great potential in storing large amounts of hydrogen efficiently. However, this technology is relatively new and requires a clear understanding. Therefore, a quick review of underground hydrogen storage is needed to understand its fundamental concepts. This review article presents important components relevant to underground hydrogen storage. First, some currently available hydrogen production methods are discussed followed by hydrogen storage methods. Both small-scale and large-scale hydrogen storage methods are presented. Next, some important factors (fluid properties, rock properties, solid-fluid interactions, and chemical interactions) influencing underground hydrogen storage are summarized. This is followed by presenting various interesting field studies for underground hydrogen storage. Lastly, some challenges and future outlooks pertinent to underground hydrogen storage are reviewed. This article will serve as a useful resource that provides a quick overview of underground hydrogen storage for both researchers and industrialists. © 2023 American Chemical Society. All rights reserved.