  Young neutron stars (NSs) have magnetic fields $B$ in the range
$10^{12}-10^{15}$ G, believed to be generated by dynamo action at birth. We
argue that such a dynamo is actually too inefficient to explain the strongest
of these fields. Dynamo action in the mature star is also unlikely. Instead we
propose a promising new precession-driven dynamo and examine its basic
properties, as well as arguing for a revised mean-field approach to NS dynamos.
The precession-driven dynamo could also play a role in field generation in
main-sequence stars.
