  We reformulate the interpretation of the mean-field glass transition scenario
for finite dimensional systems, proposed by Wolynes and collaborators.
  This allows us to establish clearly a temperature dependent length xi* above
which the mean-field glass transition picture has to be modified. We argue in
favor of the mosaic state introduced by Wolynes and collaborators, which leads
to the Adam-Gibbs relation between the viscosity and configurational entropy of
glass forming liquids.
  Our argument is a mixture of thermodynamics and kinetics, partly inspired by
the Random Energy
  Model: small clusters of particles are thermodynamically frozen in low energy
states, whereas large clusters are kinetically frozen by large activation
energies. The relevant relaxation time is that of the smallest `liquid'
clusters. Some physical consequences are discussed.
