  The question of the degree of order in the magnetic fields of relativistic
jets is important to any understanding of their production. Both vector-ordered
(e.g. helical) and disordered, but anisotropic fields can produce the high
observed degrees of polarization. We outline our models of jets in FR I radio
galaxies as decelerating relativistic flows. We then present theoretical
calculations of the synchrotron emission from different field configurations
and compare them with observed emission from FR I jets. We show that
large-scale helical fields (with significant poloidal and toroidal components)
are inconsistent with observations. The combination of an ordered toroidal and
disordered poloidal component is consistent with our data, as is an entirely
disordered field. Jets must also contain small, but significant amounts of
radial field.
