The article considers the stages of development of the theory of the method of incoherent scattering as one of the methods of studying the ionosphere. The preconditions for the establishment of scientific centers for ionosphere observation by the method of incoherent scattering, the creation and development of an experimental research base and the formation of a global network of such institutions are highlighted. The idea of ​​the HP method belongs to the American scientist William Gordon. The HP method has become the most informative and accurate method of studying almost all the characteristics of the ionosphere. It made it possible to measure the electron concentration below and above the main maximum, which was impossible with vertical sounding. The advantage of the HP method is that a significant number of characteristics of the ionosphere could be measured simultaneously in a significant range of altitudes. This equates to launching a well-equipped geophysical missile. The duration of such studies compared to episodic missile observations makes this method unique. Today the method is considered the most informative and accurate.