Part I. The Landscape, Implications, and Assumptions -- Chap 1. The Digital Twin: Why and What? -- Chap 2. DT and Digital Revolution -- Chap 3. Business models design for the Digital Twin -- Chap 4. The evolution and history of the Digital Twin -- Part II. Technologies -- Chap 5. Representing the DT: New devices, new interfaces -- Chap 6. Where the data come from? Relation between IoT and DT -- Chap 7. AI for DT: from data to knowledge -- Chap 8. Simulation -- Chap 9. Architectures and Implementations -- Chap 10. Network for Digital Twin -- Chap 11. Managing the unmanageable -- Chap 12. Security and DT -- Section III The Digital Twin in Operation -- Chap 13. Making the DT Operational in Enterprise Processes -- Chap 14. Making the DT Operational in a Large Ecosystem -- Section IV Vertical Domains for Digital Twin Applications -- Chap 15. The Digital Twin in Manufacturing -- Chap 16. The Digital Twin for Operations, Maintenance, Repair, and Overhaul -- Chap 17. The Digital Twin for Display, Education, and Curation -- Chap 18. Prognostication and Prediction, Prevention, and Prescription -- Chap 19. The Digital Twin in Human Activities and Nature: the eHealth example -- Chap 20. The Digital Twin in Complex Systems -- Section V Conclusion -- Chap 21. Future Evolution of the Digital Twin -- Chap 22. DT in Action and lesson learnt.