With a growing world population and changing climate conditions, cities have many problems to face in the future. The changing climate can affect the way we appropriate urban outdoor spaces which will affect the social sustainability in the city, so adaptation strategies in cities are necessary. Urban designers should create conditions to maintain the quality of life in these spaces and therefore the question is asked: “How can urban design improve the urban microclimate of- and (temporary) appropriation in urban outdoor spaces to make Milan sustainable towards 2100? This thesis is in search of urban design solutions for a social- and environmentally sustainable development of cities in the future. To achieve this the thesis will elaborate at first on temporary appropriation and the guidelines that urban designers should take into account to create (a) pleasant walkability, places for staying and soft edges. Secondly, it will elaborate on urban microclimate and it’s guidelines. Thirdly, and most importantly, the relations between appropriation and urban microclimate will be explained. Through a strong analysis of the theoretical subjects and an analysis of Milan as a case study a vision and design strategy is developed. On different spatial scales, the projects show the opportunities and necessary actions that should be taken to create a sustainable living environment towards 2100. Design methods are used to research how urban designers can make the spatial translation of the theoretical guidelines and these solutions are shown in a handbook called: “Climability solutions for urban design”. These solutions have been applied to multiple project locations in Milan where is shown how the solutions work, who is involved and which necessary actions are needed. After all, to create a sustainable environment towards 2100 interventions on different scale levels should be designed with great attention to the urban microclimate and appropriation of urban outdoor spaces. Designers should be more climate aware and should integrate choice in their design where people should have many opportunities to appropriate the space and to choose a microclimate that is pleasant for them. This research can be extended by site visits with interviews of residents and professionals in the fields of social- and environmental sustainability. Moreover, more extensive use of design tools, like ENVI-met, will give more insight into the design of urban microclimate and will improve the design ideas.