This paper refers to the regulation as an instrument of administrative intervention in an overview of liberalization of essential utilities, especially in the electricity industry. From this perspective, we examined the transformation undergone by the state's relationship with society, due to the new economic paradigm, which promotes a liberalized economy for the electricity supply, regulated by independent agencies that intervene in the energy market, without participating in it. Finally, we analyse the relationship between the independent energy regulator and the antitrust system, with the purpose of achieving the suitable functioning of energy markets. The study was done from the evolution of the Spanish electricity sector.