In the context of this theoretical master’s a new, sustainable concept of district development was developed: the transformation area. The aim was to show how sustainable urban districts, which set impulses for surrounding neighborhoods and thus contribute to positive change, may be de­veloped in medium-sized towns. To achieve this purpose three hypotheses have been assumed: a transformation area should be devel­oped on an urban brownfield site; it should comprise a mixture of typologies, open areas and uses, while taking process features and the three dimensions of sustainable devel­opment into account. These hypotheses shall help answer the paramount research question “Which planning components are needed in medium-sized cities in order to initiate sustainable development in newly developed areas and their neighborhoods?”. In order to answer the research question, findings from literature were consulted and three case studies were examined by means of brief urban district profiles. The latter were achieved and analyzed by on-site inspections, eligible maps and qualitative interviews. The evaluation of the analysis reveals that some proven planning components like communal living concepts or easy access to local amenities may be adopted for the concept of a trans­formation area. Other components, however, like a comprehensive energy strategy need to be added in order to face future challenges and initiate real change. An exemplary strategy for a transformation area in the medium-sized town of Kerpen has been developed in order to apply the previously compiled 16 components to a concrete area. This example reveals how change around this area can look like, namely in form of shorter ways and easy access to multiple uses, more places for social exchange, but also in form of a climate friendly generation of energy. Finally, a critical assessment of all findings shows that challenges such as the initiative of the citizens and the financing of such projects have to considered in practice.