  Jets are ubiquitous in the star-forming process since accretion is intimately
associated with outflow. Weak free-free continuum emission in the centimeter
domain is associated with these jets.
  Observations in the cm range are most useful to trace the base of the ionized
jets, close to the YSO and its accretion disk, where jets are accelerated and
collimated. Optical or near-IR images are obscured by the high extinction
present. Radio recombination lines in jets (in combination with proper motions)
should provide their 3D kinematics. SKA will be crucial to perform this kind of
observations.
  Thermal radio jets are associated with both low and high mass protostars. The
ionizing mechanism appears to be related to shocks in the associated outflows,
as suggested by the observed correlation between the centimeter luminosity and
the outflow momentum rate. From this correlation and that with the bolometric
luminosity of the driving star it will be possible to discriminate with SKA
between unresolved HII regions and jets, and to infer physical properties of
the embedded objects.
  Some jets show indications of non-thermal emission (negative spectral
indices) in their lobes. Linearly polarized synchrotron emission has been found
in the lobes of the jet of HH 80-81, allowing us to measure the direction and
intensity of the magnetic field, a clue ingredient in determining the jet
collimation and ejection mechanisms. As only a fraction of the emission is
polarized, very sensitive observations such as those that will be feasible with
SKA are required to perform these studies in other objects.
  Jets are common in many kinds of astrophysical scenarios. Characterizing YSO
radio jets, whose physical conditions can be reliably determined from their
thermal emission, would be also useful in understanding acceleration and
collimation mechanisms in all kinds of astrophysical jets.
