  The next generation of very long baseline interferometry (VLBI) is stepping
into the era of microarcsecond ($\mu$as) astronomy, and pushing astronomy,
especially astrometry, to new heights. VLBI with the Square Kilometre Array
(SKA), SKA-VLBI, will increase current sensitivity by an order of magnitude,
and reach astrometric precision routinely below 10 $\mu$as, even challenging 1
$\mu$as. This advancement allows precise parallax and proper motion
measurements of various celestial objects. Such improvements can be used to
study objects (including isolated objects, and binary or multiple systems) in
different stellar stages (such as star formation, main-sequence stars,
asymptotic giant branch stars, pulsars, black holes, white dwarfs, etc.),
unveil the structure and evolution of complex systems (such as the Milky Way),
benchmark the international celestial reference frame, and reveal cosmic
expansion. Furthermore, the theory of general relativity can also be tested
with SKA-VLBI using precise measurements of light deflection under the
gravitational fields of different solar system objects and the perihelion
precession of solar system objects.
