  We present a discussion of the partial Paschen-Back (PB) effect in magnetic
Ap stars. An overview of the theory is illustrated with examples of how
splittings deviate non-linearly from the simple Zeeman picture; normally
forbidden ``ghost lines'' appear in strong fields. Resulting asymmetric stellar
Stokes profiles for a dipolar magnetic geometry are shown for the FeII 6149
line and it is established that PB lines may be subject to wavelength shifts.
Modelling of Stokes profiles in the PB regime opens exciting new diagnostics.
