  We review recent relativistic hydrodynamic simulations of jets, and their
interpretation in terms of the results from linear stability analysis. These
studies show that, interpreted naively, the distribution of synchrotron
intensity will in general be a poor guide to the physical state (density and
pressure) of the underlying flow, and that even if the physical state can be
inferred, it, in turn, may prove to be a poor guide to the source dynamics, in
terms of the transport of energy and momentum from the central engine. However,
we demonstrate that an interplay of simulation and linear stability analysis
provides a powerful tool for elucidating the nature and character of structures
that jets may sustain. From such studies we can explain the complex behavior of
observed jets, which manifest both stationary and propagating structures,
without recourse to ad hoc macroscopic disturbances. This provides a framework
for the interpretation of multi-epoch total intensity data wherein an
understanding of the character of individual flow features will allow the
effects of physical state and dynamics to be deconvolved.
