Digital twin technology allows creating virtual models of real-world systems that can be used to assess current performance, predict faults, and simulate future changes. A digital twin must answer what is happening now, what could happen, and what should happen next. They have applications in manufacturing, healthcare, energy, and more. Enabling technologies include the Internet of Things, cloud computing, artificial intelligence, and augmented/mixed/virtual reality. While digital twins provide benefits like improved optimization and reduced downtime, challenges to adoption include issues with connectivity, data security, cost awareness, and expectations that the technology can solve all problems. The global digital twin market is projected to grow significantly in coming years.