The glass transition is well known to glass makers or from the common ex- perience of drying a used chewing gum. A liquid melt or a rubber becomes a solid glass when its temperature is lowered or a solvent is extracted without crystallization. There are also dynamic effects. The viscosity of a liquid is small at high temperatures but increases dramatically as cooling proceeds down to the glass temperature T - The increase is continuous and amounts g to about fifteen orders of magnitude The technical importance of the glass transition cannot be overestimated. A few examples will be presented...