Over the past two decades, public utilities (gas, electricity, railway, telecommunications, water supply), an integral part of which are natural monopoly segments, have undergone major changes.  They went in the direction of deregulation, introduction of competition, modernization of functions and methods of regulation. Reforms have begun in Russia, but the reform models have not yet acquired completed forms. In this regard, trends in the development of theoretical concepts underlying practical transformations are of great interest. In this article we want to draw attention to those fundamentally important shifts in the theory of natural monopoly and the Economics of regulation, which formed the basis and prepared the ongoing transformation in recent decades.