  Our understanding of the mechanism by which topological defects are formed in
symmetry breaking phase transitions has recently changed. We examine the
non-equilibrium dynamics of defect formation for weakly-coupled global O(N)
theories possessing vortices (strings) and monopoles. It is seen that, as
domains form and grow, defects are swept along on their boundaries at a density
of about one defect per coherence area (strings) or per coherence volume
(monopoles).
