Glass is reviewed from fabrication to application, laying emphasis on the wide-ranging physics involved. This begins with liquids and solids and the way in which glasses are defined and can be demonstrated in the classroom. At the atomic level the regular structure of crystals and their irregular counterparts in glasses are explained through easy-to-teach toy models. A future article will describe applications of glasses from optical fibres to self-cleaning windows. The intention throughout is to emphasize the rich resource that glass can provide in class for teaching physics holistically.