Astrophysical masers are associated with regions of star formation,with the circumstellar gas of late-type giants and supergiants, and with gas at the nuclei of galaxies---including that in accretion disks around massive black holes. The general properties of astrophysical masers will be surveyed briefly. Basic ideas about physical
processes involved in the creation and transport of astrophysical maser radiation will be summarized. I will then report on calculations
in selected areas of current activity---(a)the polarization of the radiation and its possible conection with MHD turbulence, and (b)the images and spectra of masing, Keplerian disks.
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