On the one hand, energy utility companies (EUCs) fulfill public tasks assigned to them by the state. On the other hand, they are also often active as entrepreneurs in the free market. For example, they supply electricity products to major customers, install photovoltaic and e-mobility systems and provide services in the areas of building technology, metering and telecommunications. In such private sector activities, energy utility companies potentially enjoy unjustified advantages due to the fact that they are publicly controlled and perform public tasks: they receive particularly good financing conditions, are taxed on a privileged basis and benefit from economies of scope and information advantages when public and private sector tasks are carried out in parallel. Such privileges may distort competition or prevent companies from entering a market. This chapter examines the legal requirements for dealing with this issue and proposes specific measures with which legislators and authorities can avoid harmful effects of private sector activities by EUCs.