The article examines the constitutional duty to provide protection against changes to the regulatory framework when the owners of industrial plants had been encouraged to undertake investments in their plants. Generally, the fundamental right to property (Art. 14 sec. 1 GG) does not protect against changes to the general regulatory framework with regard to economic activity and their effect on market opportunities. However, as the Bundesverfassungsgericht stated only recently, Art. 14 sec. 1GG can, under certain conditions, provide protection in cases known as “frustrated investments”. Although there is no guarantee for the fulfilment of all expectations with regard to an investment, investments in property undertaken in legitimate reliance on a legal situation may require to be considered in light of the principle of proportionality – regarding the questions whether and how owners should get compensation for devalued investment in cases where the legislature limits the further use of the property directly or to a significant extent.