Glasses can be defined as non-crystalline solids with a disordered liquid-like structure. After recalling the concepts of order and disorder in various states of aggregation of matter, the problem of glass formation by quench of melt is described as well as other ways of obtaining disordered solids. The evolution of the technology of glass-making is outlined and various applications of traditional and novel glasses are presented. The extraordinary development of glasses, which are essential in a modern economy, can be explained by the fact that these non-crystalline materials combine the properties of their parent crystals with those of liquids where the constraints linked with order are no longer present.