AbstractI discuss the effect of accretion on the magnetic field of an accreting white dwarf. Whereas the magnetic fields of isolated white dwarfs are not expected to change significantly with time, I show that if an accreting white dwarf increases in mass at a rate > 1–5 × 10⁻¹⁰M_Θ yr^–1, accretion overcomes ohmic diffusion and has a significant effect on the field structure. I discuss the implications of this result for observed systems. In particular, accretion induced field evolution may provide the missing evolutionary link between the strong field, slowly accreting AM Her systems and the weak field, more rapidly accreting intermediate polars.