  Jet-driven shocks are responsible for an important fraction of the emission
of the narrow-line regions (NLRs) in many classes of AGN. However, this cannot
explain all observations. It is clear that the remaining sources are
photoionised by the active nucleus. The 2-d hydrodynamic models from the RSAA
group support an evolutionary scenario whereby the shock-excited NLRs are
initially jet-driven but later, ionizing photons from the central engine
replace shocks as the main excitation mechanism and shock induced star
formation may also become important. In their photoionized phase, dusty and
radiation-pressure dominated evolution produces a self-regulated NLR spectrum.
This model aso explains the coronal emission lines and fast (3000 km s$^{-1}$)
outflows seen in some Seyferts.
