  Observations made with the VLBA have led to fundamental advances in our
understanding of how radio jets in AGN evolve from parsec-scales out to
distances exceeding several hundred kiloparsecs. In this review I discuss
current models of young radio source evolution, as well as the observational
evidence for a rapid change in jet properties on scales of ~1 kpc. A central
topic of current debate is the relative importance of intermittent jet fueling
versus jet-environment interactions in causing a drop-off in powerful radio
sources at this critical evolutionary stage. Recent 3-D hydrodynamical jet
simulations suggest that dense environments and cloud collisions can
temporarily stifle, but not completely halt powerful relativistic jets. Several
VLBA studies of jet-ISM interactions in both blazars and weak Seyfert jets have
indicated that collimated outflows are indeed possible in dense environments.
At present, the bulk of the evidence favors intermittent AGN accretion as the
dominant factor in determining the evolutionary path of large numbers of AGN
jets.
