The global smart cities market size was valued at USD 1,226.9 billion in 2022 and is expected to register a compound annual growth rate (CAGR) of 25.8% from 2023 to 2030. Firstly and visually, a smart city is a city that has no traffic jams. In the smart cities, both information and communication technologies are integrated for exchanging real-time data between their citizens, governments, and organisations. Blockchain has been considered as the key driver for development of smart cities. Blockchain technology can provide high security for large communications and transactions between many stakeholders in the smart cities. In addition, digital twins are also considered as the starting key for construction of smart cities. Digital twin refers to a simulation of physical products in virtual space. This simulation makes full use of physical models/wireless sensor networks/ historical data of city operation to integrate big information (digital twin cities) under multi-discipline, multi-physical quantities, multi-scale, and multi-probability. Digital Twin, Blockchain, and Sensor Networks in the Healthy and Mobile City explores how digital twins and blockchain can be used in smart cities. Section 1 deals with their promising applications for safe and healthy cities, respectively. Section 2 covers other promising applications and current perspectives of blockchain and digital twin for future smart cities. Together with its companion volume, Digital Twin, Blockchain, and Sensor Networks in the City, this book will help us make sense of the vast amount of data around the city, and will guide us to use that data to create happy, healthy, safe and productive lives.