Lithium metal batteries possess remarkable energy storage capabilities, but their commercial realization is hindered by challenges in controlling the reactivity of lithium. Interfacial engineering has emerged as a promising strategy for addressing lithium reactivity. In this article, we discuss several key interfacial engineering approaches used to stabilize lithium metal at lithium–electrolyte and lithium–current collector interfaces. We examine these commonly employed interfacial engineering methods and highlight unresolved questions crucial for advancing the understanding of lithium reactivity. Our discussion highlights the potential of interfacial engineering tools to enhance our understanding of and overcome the challenges associated with lithium reactivity.