This open access book examines collaborative approaches to urban transformation processes and guides smart co-design applications in such contexts. It presents a selection of co-design methods that can be fruitfully integrated with mobile applications, focusing on the CitySense app, the result of two H2020 European Projects. This innovative solution favours a virtuous co-creation process involving decision-makers, architects, developers, and citizens. It provides a service for assessing the existing urban context and possible design solutions from the community perspective. It enables the study of citizens’ perceptions by pairing Augmented and Virtual Reality with the “Experiential Environmental Impact Assessment: exp-EIA©” method, which integrates psychological and architectural perspectives. This approach shapes all phases of the design process, encouraging evidence-based design and decision-making, and also supports the definition of a proper design brief before investing and the pre-assessment of the urban design project’s experiential outcomes before construction. The book starts by presenting the evolution of citizens’ involvement from traditional to smart solutions, and then provides a general framework of co-design options using smart applications (especially the CitySense app). The overall approach fosters a phygital (physical + digital) approach by outlining possible ways of enhancing fruitful public/private collaborations with a view to making shared, high-performance urban decisions.