The vibronic origin of ferroelectricity and structural phase transitions first suggested three decades ago, has been given recently new theoretical foundation and strong experimental evidence. It has been shown that for any polyatomic system, including crystals, the vibronic mixing of the ground electronic state of the high-symmetry reference configuration with the excited states by low-symmetry nuclear displacements is the only source of instability of this configuration, and that visually the main contribution to this effect is due to the formation of new covalent binding by distortion. The proof of this statement allowed us to show that the driving force for ferroelectric distortions of the lattice, the vibronic coupling, is of local origin. The long-range Coulomb interactions are important in that they may soften the lattice, but they don't produce instability. It is shown that the interplay of local instability enhanced by long-range forces with the entropy factor that requires disorder at T ≠ 0, may result in formation of linearchain ordered clusters in the disordered phases. A qualitative explanation of the origin of basic tetragonal distortions in PbTiO3 as due to the influence of the lone pairs (6s)2 of the Pb2+ ions is also given. Experimental results of different nature (X-ray diffraction and diffuse scattering, ESR with probing ions, XAFS experiments, femtosecond resolution of soft-mode dynamics, etc.) strongly confirm the main predictions of the vibronic theory about the local origin of the distortions and the order-disorder character of phase transitions in BaTiO3, KNbO3, and PbTiO3.