The Lindemann criterion states that melting occurs because of "vibrational instability", e.g. crystals melt; when the average amplitude of thermal vibrations of atoms is relatively high compared with interatomic distances, e.g. < δu > > δ L R s, where δu is the atomic displacement, the Lindemann parameter δ L ≈ 0.20...0.25 and R s is one-half of the inter-atomic distance. The "Lindemann melting criterion" is supported by experimental data both for crystalline materials and for glass-liquid transitions in amorphous materials.