Chapter 5 explores the use of distributed ledger technologies in cities to help improve citizen-centric services: land registries, health care, welfare payments, identity, supply chains, and voting. McKinsey analysts predict that by 2020 the number of smart cities will reach 600 worldwide, and 5 years later almost 60% of the world's GDP will be produced in them. Digital technologies could become an engine of economic progress, and Blockchain could be one of those technologies. This connectivity, however, comes at a cost. How will cybersecurity evolve with Web 3.0 and 4.0 technologies to protect cities from cyber-attacks? This chapter introduces how Blockchains may be used to resolve a range of city-based challenges arising from broader global concerns like national population increases, urban density, anthropomorphic climate change, urban pollution and mobility, local and national citizen services, and infrastructure.