Interoperability is what allows different systems to communicate, both on technological (e.g. hardware and software) and societal grounds (i.e., to connect users’ experiences over internet or ease collaboration between institutions). To achieve the seamless exchange of information, interoperability entails the establishment of standards and technical requirements that could either be realized through spontaneous efforts by market participants or imposed by the law. Building on the assumption that technical specifications are key to make interoperability happen, this chapter aims to show that interoperability plays a fundamental role in realizing the metaverse and shaping its governance. More specifically, we show that interoperability is the watershed between existing walled virtual worlds (i.e., the building blocks of the metaverse), and a mature, fully-functioning metaverse. Even more, interoperability contributes to define the very governance of virtual environments and the markets the metaverse creates. Hence, striking a balance between industry-defined standards and regulatory intervention is essential to define a good governance.