BFallow land is growing. This finding is undisputed. Nationwide there is a fallow area of ​​well over 100,000 ha. These land resources need to be reactivated for future settlement development and to protect open spaces. The reuse of fallow land not only poses new challenges for spatial and urban planning, but also for the legal management of the associated planning and other legal issues. After taking stock of the current availability of, in particular, urban fallow land, Christof Austermann examines the existing legal instruments for the rededication of these areas. This is followed by recommendations for action in dealing with fallow land in practice and the development of legislative proposals to promote the reactivation of fallow land, and the interests of planning practice are also incorporated into the work.