  This review surveys the observed properties of interstellar dust grains: the
wavelength-dependent extinction of starlight, including absorption features,
from UV to IR; optical luminescence; IR emission; microwave emission; optical,
UV, and X-ray scattering by dust; and polarization of starlight and of infrared
emission. The relationship between presolar grains in meteorites and the
interstellar grain population is discussed. Candidate grain materials and
abundance constraints are considered. A dust model consisting of amorphous
silicate grains, graphite grains, and PAHs is compared with observed emission
and scattering. Some issues concerning evolution of interstellar dust are
discussed.
