  Cold Dark Matter with a large cosmological constant (LambdaCDM) appears to
fit large scale structure observations well. Of the possible small scale
problems, the Central Cusps and Too Many Satellites problems now appear to be
at least partly solved, so Angular Momentum has become the most serious
remaining CDM problem. There are actually at least two different angular
momentum problems: A. Too much transfer of angular momentum to the dark halo to
make big disks, and B. Wrong distribution of spedific angular momentum to make
spiral galaxies, if the baryonic material has the same angular momentum
distribution as the dark matter. The angular momentum of dark matter halos, and
presumably that of the galaxies they host, appears to arise largely from the
orbital angular momentum of the satellites that they accrete. Since the dark
and baryonic matter behave very differently in such accretion events, it is
possible that the resulting angular momentum distribution of the baryons is
different from that of the dark matter, as required to make the sort of
galactic disks that are observed. The latest hydrodynamical simulations give
some grounds for hope on this score, but much higher resolution simulations are
needed.
