A city’s morphology depends on the urban blocks that make up the city’s DNA. Historically urban blocks were designed for the people to live and create community spaces and these have since evolved over time and thus are sustainable in the way they grow and are reused, rehabilitated, and renewed. This study helps us understand what makes an urban block sustainable and how it can be designed to be sustainable through the examples of London (evolutionary adaptive reuse), Amsterdam (grassroots planning), and Barcelona (Superblocks with tactical urbanism). The study is substantiated by data collected with the help of surveys and comprehensive studies done on these major cities. A list of parameters of factors that make a city block sustainable has been collated to assist the design of future urban blocks that works sustainably from the designing stage to the way it works as an urban environment.