  A disorder parameter is constructed which signals the condensation of
vortices. The construction is tested by numerical simulations. Advances in the
understanding of the basic properties of QCD vacuum will be reported. Three
main subjects will be touched: 1) Condensation of monopoles and confinement. 2)
Topology, or instanton physics. 3) Gauge invariant field strength correlators,
and their behaviour across the deconfining phase transition.
