  We review recent observations of circularly polarized radiation from AGN made
with the VLBA and with the ATCA. We also discuss briefly the detections of the
Galactic sources Sag A* and SS433. The origin of the circular polarization is
still an open question in most cases, and we discuss four possible mechanisms.
Detectable circular polarization is a common property of quasars, but not of
radio galaxies, and is always associated with the compact core. There is
growing evidence that the sign of the circular polarization stays the same over
at least two or three decades in time, suggesting it is a fundamental property
of the jet.
