With the creation of massive data in projects, the digitization/computerization of various stages and processes of built environments are emerging to have a broad influence on how the architecture, engineering, and construction (AEC) projects are planned, built, and managed. With the evolution of Big Data and model-based engineering, the next logical step is to introduce the concept of Digital Twin, extending model-based paradigms along the complete lifecycle. Digitalization and computerization of data and information flow have a broad influence on the system and process of managing the lifecycle of projects. The relation among the DT and smart cities has been recognized as the novel and ultimate technological apparatus for smartening cities. Blockchain empowers the security of the DT system through cryptographic hashing algorithms. This process is possible by storing DT data on distributed ledgers that cannot be changed easily and cannot be controlled by any central authority. DT encompasses sensors, measurement technologies, internet of things, simulation, and modeling and ML.