Digital Twin (DT) technologies are envisioned to bring substantial benefits to industry by optimizing production processes, thus reducing the costs and time-to-market of products. A DT is a digital representation of a real-world entity which we call the Physical Twin (PT). The DT and PT are connected by a communication infrastructure which allows the DT to maintain a known level of fidelity to the PT it represents. A DT leverages the models at its core to offer its stakeholders a range of services that add value to the PT without unduly compromising the PT’s operation. These services could include visualization and monitoring, predictive maintenance, fault diagnosis, what-if analysis and runtime reconfiguration of the PT. The key concepts behind DTs, as well as ways to obtain services from them in industrial settings, coupled with reports on existing case studies, are the main topics covered in this chapter.