  I review my work with Bruce Draine on dust emissivity at microwave
frequencies (3 cm - 3 mm). This emissivity explains the recently detected
"anomalous" component of the galactic foreground emission. Both small (a<0.001
micron) and large grains contribute to this emission. Small grains have
electric dipole moments and emit while they rotate; the microwave emission of
large grains is mostly due to magneto-dipole radiation. Most efficient
magneto-dipole emitters are strongly magnetic, e.g. ferrimagnetic or
ferromagnetic, materials. The relative role of the two mechanisms can be
established through observations of microwave emissivity from dark clouds. New
microwave window is a window of opportunity for interstellar studies. Magnetic
fields inside dark clouds may be successfully studied via microwave
polarization. Microwave emissivity constrains the abundance of strongly
magnetic materials. For instance, the available data at 90 GHz indicate that
not more than 5% of interstellar Fe is in the form of metallic iron grains or
inclusions (e.g., in ``GEMS''). Future missions, e.g. MAP and PLANCK, will
bring a wealth of microwave data that can be successfully used to study ISM.
Such a study would be appreciated by cosmologists who franticly try to remove
all foregrounds from their data.
