These articles are the final results of an investigation of solid-state phase transitions undertaken by Yuri Mnyukh in 1959. From a number of key experimental discoveries the universal nucleation-and-growth molecular mechanism of phase transitions was deduced. It turned out to be the universal tool to unravel the physical nature of several basic phenomena of solid-state physics. The second-order phase transitions were shown to be nonexistent. The origin of ferromagnetism was accounted for. The molecular mechanism of ferromagnetic transitions, as well as of the magnetization process was described. The origin of ferroelectricity and its similarity to ferromagnetism was uncovered. The mechanism of phase transitions in superconductors was specified. The great enigma - "heat capacity lambda-anomalies" in solids and liquid He - was eliminated. The reader will find all that and more in this book.