  Cold dark matter (CDM) models predict small-scale structure in excess of
observations of the cores and abundance of dwarf galaxies. These problems might
be solved, and the virtues of CDM models retained, even without postulating
{\it ad hoc} dark matter particle or field interactions, if the dark matter is
composed of ultra-light scalar particles (m ~ 10^{-22}eV), initially in a
(cold) Bose-Einstein condensate, similar to axion dark matter models. The wave
properties of the dark matter stabilize gravitational collapse providing halo
cores and sharply suppressing small-scale linear power.
