Open-source enables products and services to bring choice, technology, and community to our customers. Microsoft has published open-source GitHub repositories for smart building, smart city, and smart grid ontologies for digital twins, expressed in the open Digital Twins Definition Language (DTDL). We are excited to share this work with the Digital Twin Consortium’s s Open-Source Collaboration community. It’s our goal to partner with industry experts and provides ontologies which learn from, build on, and/or use industry standards, meet the needs of developers, and are adopted by the industry.