  Secular evolution and fueling is driven by bars in spiral galaxies, and the
related dynamical processes are reviewed. It is shown that gravity torques
dominate over viscous torques, and produce gas infall to the center. In this
infall, the bar wave accepts the angular momentum, which produces its
destruction. In the end, a central mass concentration is build, which also
contributes to this destruction. While gas can be stalled at ILR for a while,
secondary bars then take over the fueling. In a galaxy life-time, several bar
episodes can successively develop. Through external gas accretion, disks are
replenished by intermittence, between two bar phases. While the general trend
for a galaxy is to evolve towards early-types, its morphology can oscillate,
and turn back transiently to later-types.
