  Recent progresses in the description of glassy relaxation and ageing are
reviewed for the wide class of network-forming materials such as $GeO_2$,
Ge$_x$Se$_{1-x}$, silicates (SiO$_2$-Na$_2$O) or borates (B$_2$O$_3$-Li$_2$O),
all of them having an important usefulness in domestic, geological or
optoelectronic applications. A brief introduction of the glass transition
phenomenology is given, together with the salient features that are revealed
both from theory and experiments. Standard experimental methods used for the
characterization of the slowing down of the dynamics are reviewed. We then
discuss the important role played by aspect of network topology and rigidity
for the understanding of the relaxation of the glass transition, while also
permitting analytical predictions of glass properties from simple and
insightful models based on the network structure. We also emphasize the great
utility of computer simulations which probe the dynamics at the molecular
level, and permit to calculate various structure-related functions in
connection with glassy relaxation and the physics of ageing which reveals the
off-equilibrium nature of glasses. We discuss the notion of spatial variations
of structure which leads to the picture of "{\em dynamic heterogeneities}", and
recent results of this important topic for network glasses are also reviewed.
