Cities are rapidly growing. There is an assumption that 90% of global population growth will be in cities between now and 2030. Therefore, infrastructures and the environment have to be adapted to the changing demands. Moreover, new urban development strategies have to be elaborated. In 2007, the first international Visualization Summit of more than 100 international researchers and practitioners stated a jointly developed research goal for the year 2010, namely ’Visualizing Future Cities’. Therefore in this chapter we provide an overview about visualization methods, decision support tools in architecture, urban and regional planning, stakeholder participation and collaborative environments. Also, new decision support tools for the visualization of future cities will be introduced.