<p>Lambda-peak in heat capacity is common in many phenomena (magnetism, superfluidity in liquid helium, ordering–disordering in alloys, etc.). Mathematical description of its shape does not exist. Raw calorimetric data are treated with using empirical power and exponential polynomials with coefficients without physical meaning. The history of genesis and development of theory of magnetic phase transitions is traced in order to reveal the reasons of its unsuccessful current state. The points preventing from the solution to the problem of lambda-peak in heat capacity of ferromagnetics at the Curie point are described. Most popular formulas for magnetization, Ehrenfest classification of phase transitions, and the theory of critical indices are shown to misguide in the search for the mathematical description of the lambda-peak of heat capacity. Excluding these obstacles from the consideration will allow us to solve the problem.</p>