  The jets observed to emanate from many compact accreting objects may arise
from the twisting of the magnetic field threading a differentially rotating
accretion disk which acts to magnetically extract angular momentum and energy
from the disk. Two main regimes have been discussed, hydromagnetic outflows,
which have a significant mass flux and have energy and angular momentum carried
by both matter and electromagnetic field and, Poynting outflows, where the mass
flux is negligible and energy and angular momentum are carried predominantly by
the electromagnetic field. We describe recent theoretical work on the formation
of relativistic Poynting jets from magnetized accretion disks and new
relativistic, fully-electromagnetic, particle-in-cell simulations of the
formation of jets from accretion disks.
