  Aligned non-spherical dust particles polarize starlight passing through the
dust cloud. They also emit polarized far infrared and sub-mm radiation.
Substantial progress in understanding of grain alignment theory makes the
interpretation of the polarized radiation in terms of underlying magnetic
fields much more reliable. I discuss a number of fundamental processes that
affect grain alignment. In particular, I shall discuss how subtle effects
related to nuclear spins of the atoms alter the dynamics of dust grains. I
shall discuss how the theory explains the existing observational data and
demonstrate when the polarization can and cannot be interpreted in terms of the
underlying magnetic fields.
