  We discuss the rotational excitation of small interstellar grains and the
resulting electric dipole radiation from spinning dust. Attention is given to
excitation and damping of rotation by: collisions with neutrals; collisions
with ions; plasma drag; emission of infrared radiation; emission of microwave
radiation; photoelectric emission; and formation of H_2 on the grain surface.
We introduce dimensionless functions F and G which allow direct comparison of
the contributions of different mechanisms to rotational drag and excitation.
Emissivities are estimated for dust in different phases of the interstellar
medium, including diffuse HI, warm HI, low-density photoionized gas, and cold
molecular gas. Spinning dust grains can explain much, and perhaps all, of the
14-50 GHz background component recently observed in CBR studies. It should be
possible to detect rotational emission from small grains by ground-based
observations of molecular clouds.
