  White dwarfs rotate. The angular momentum in single white dwarfs must
originate early in the life of the star, but also must be modified (and perhaps
severely modified) during the many stages of evolution between birth as a
main--sequence star and final appearance as a white dwarf. Observational
constraints on the rotation of single white dwarf stars come from traditional
spectroscopy and from asteroseismology, with the latter providing hints of
angular velocity with depth. Results of these observational determinations,
that white dwarfs rotate with periods ranging from hours to days (or longer),
tells us that the processes by which angular momentum is deposited and/or
drained from the cores of AGB stars are complex. Still, one can place strong
limits on these processes by considering relatively simple limiting cases for
angular momentum evolution in prior stages, and on subsequent angular momentum
evolution in the white dwarfs. These limiting-case constraints will be reviewed
in the context of the available observations.
