As hydrogen becomes more prominent in the portfolio of technologies for reducing carbon emissions, more attention has been directed towards its safe transport, storage, and end use. Most hazard scenarios involve the unintended release of hydrogen, which can result from improper design, assembly, or operation of hydrogen containment systems. One important aspect of design is the selection of materials, particularly those comprising the pressure boundaries of hydrogen containment components. From the perspective of unintended hydrogen release, materials selection is focused on two particular concerns related to hydrogen ingress: 1) hydrogen permeation rates in materials, which dictate the leak rates through pressure boundaries, and 2) the potential for hydrogen to degrade the mechanical properties of materials, which can lead to failure of pressure boundaries and sudden release of hydrogen. This article focuses on the second concern, and more specifically on the hydrogen-induced degradation of metals. In gaseous hydrogen environments at near-ambient temperatures, failure resulting from hydrogen-induced degradation of metals is typically referred to as ‘hydrogen embrittlement’.