Originally developed for enabling smart manufacturing, applications of digital twins now extend to ports, smart cities and supply chains. However, the wide range of applications results in a lack of uniform understanding of what constitutes a digital twin and how to implement it. Recent research therefore underlines the importance of standardization and interoperability as key prerequisites for building effective DT systems for complex applications. This poster thus provides an overview of the efforts of standardization bodies that foster the interoperability of digital twins.