Basic Concepts -- Thermodynamical Principles and the Landau Theory -- Order Variables, Their Correlations and Statistics: the Mean-Field Theory -- Collective Modes of Pseudospins in Displacive Crystals and the Born-Huang Theory -- Soft Modes, Lattice Anharmonicity and Pseudospin Condensates in the Critical Region -- Dynamics of Pseudospins Condensates and the Long-Range Order -- Experimental St…