  The original electronic structure of the Pb$^{2+}$ ion explains its
particular structural role in crystalline phases and silicate glasses. After a
description of the structural role of lead in crystalline phases (PbO,
silicates), this chapter presents a summary of the main structural studies
carried out on glasses from the SiO$_2$-PbO, SiO$_2$-PbO-R$_2$O (R: alkaline)
and SiO$_2$-PbO-Al$_2$O$_3$ systems, using various spectroscopic and simulation
techniques.
