  We discuss the ordering of a spin-1 condensate when quenched from its
paramagnetic phase to its ferromagnetic phase by reducing magnetic field. We
first elucidate the nature of the equilibrium quantum phase transition.
Quenching rapidly through this transition reveals XY ordering either at a
specific wavevector, or the `light-cone' correlations familiar from
relativistic theories, depending on the endpoint of the quench. For a quench
proceeding at a finite rate the ordering scale is governed by the Kibble-Zurek
mechanism. The creation of vortices through growth of the magnetization
fluctuations is also discussed. The long time dynamics again depends on the
endpoint, conserving the order parameter in zero field, but not at finite
field, with differing exponents for the coarsening of magnetic order. The
results are discussed in the light of a recent experiment by Sadler \emph{et
al.}
