  Galaxy disks evolve through angular momentum transfers between
sub-components, like gas, stars, or dark matter halos, through non
axi-symmetric instabilities. The speed of this evolution is boosted in presence
of a large fraction of cold and dissipative gas component. When the visible
matter dominates over the whole disk, angular momentum is exchanged between gas
and stars only. The gas is driven towards the center by bars, stalled
transiently in resonance rings, and driven further by embedded bars, which it
contributes to destroy. From a small-scale molecular torus, the gas can then
inflow from viscous torques, dynamical friction, or m=1 perturbations.
  In the weakened bar phases, multiple-speed spiral patterns can develop and
help the galaxy to accrete external gas flowing from cosmic filaments. The
various phases of secular evolution are illustrated by numerical simulations.
