The demographic change affects spatially very heterogeneous. Besides shrinking rural areas, especially large German cities recorded population increase. A shortage of residential space and rising rents accompany the population growth. Particularly for low income groups the access to affordable housing is difficult. The federal government has passed a law by which rents are limited in tight housing markets. The so-called »Mietpreisbremse« entered into force on 01.06.2015. In areas selected by the federal states, the rents may not exceed 10% of the local comparative rent; already existing contracts are excluded, as well as new buildings (first-time occupancy after 01.10.2014). The controversial discussion about this new regulation shows that the effectiveness of the »Mietpreisbremse« is judged critically.