The temporary, the transient, the limited, the provisional, the ephemeral describes the uniqueness of interim use. This is a phenomenon not entirely unknown in Germany. The unused is a precious and underappreciated reserve of the city. The conscious utilization of vacant spaces promotes sustainable urban development against the backdrop of socio-demographic change. The new challenges arising on social, economic, ecological, and political levels, along with the resulting questions for urban and rural areas, require solution approaches with forward-looking concepts. The aim of this scientific approach is the comprehensive identification, investigation, and understanding of the issues related to the interim use of vacant properties and brownfields, as well as their potential integration into the project development process. Methodologically and theoretically guided, the process employs qualitative research methods with exploratory and transdisciplinary content, along with the development of two application-oriented models. This dissertation explores the topic in its comprehensive complexity, going beyond merely mentioning urban planning or purely economic aspects.