The challenge of this Action Planning network is the activation of vacant buildings and building complexes for a sustainable urban development by self-organised groups. In many European cities smaller and larger derelict sites, underused premises, so called “voids” can be found in or near the city centre. These sites often have a negative impact on their surroundings, nevertheless they present a great opportunity: they can be used to complete a compact settlement structure, to provide space for needed functions in the city.