  We present a synthesis of the astronomical observations constraining the
wavelength-dependent extinction, emission, and polarization from interstellar
dust from UV to microwave wavelengths on diffuse Galactic sightlines.
Representative solid phase abundances for those sightlines are also derived.
Given the sensitive new observations of polarized dust emission provided by the
Planck satellite, we place particular emphasis on dust polarimetry, including
continuum polarized extinction, polarization in the carbonaceous and silicate
spectroscopic features, the wavelength-dependent polarization fraction of the
dust emission, and the connection between optical polarized extinction and
far-infrared polarized emission. Together, these constitute a set of
constraints that should be reproduced by models of dust in the diffuse
interstellar medium.
