Most churches and cathedrals in Britain contain stained glass: even the most unassuming buildings may have spectactular windows full of figures painted as if by coloured light. The wealth of imagery dates not only from the middle ages but also from the nineteenth century, when the majority of existing windows were made. Must of this later glass is very finely designed and of great interest. The earlier glass is rare and often not in its original position: we need to understand the intentions of the designers and craftsmen in order to appreciate it fully.