Cities and CitizenThe European Commission (EC) aims to facilitate bottom-up initiatives to speed up economic growth. For that it is necessary to empower citizens and businesses. Open data is key to this, as easy access to the right data opens the door for them to contribute as active and efficient actors in European cities. The EC-funded project Smarticipate1 , which is driven by the pilot cities of Hamburg, Rome and London, will foster citizen involvement on four levels: to join forces of committed key stakeholders, to gather local knowledge, to enable exploratory planning exercises and to create new public services. This will be realized by innovative tools, designed within Smarticipate, that provide immediate context-tailored feedback to each contribution made by citizens via online participation services. This paper outlines a novel methodology that is currently being developed within the project to co-design new public services. Our methodology enables close coordination via an iterative process with diverse urban stakeholders and end users. Citizens and businesses can create and plug their own apps for new public services into the Smarticipate platform we are developing. The overall principle is to interact in co-creation with the cities and citizens of Hamburg, Rome and London and adjust our planning and products directly to their needs. An iterative process is being carried out on three levels: participatory urban planning, usercentered design of applications and user interfaces & software engineering. The first results of this process are presented in this paper, along with an outline of the next steps.