We analyze optical and ultraviolet observations of the symbiotic binary AG Pegasi acquired during 1992-1997. The bolometric luminosity of the hot component declined by a factor of 2-3 from 1980-1985 to 1997. Since 1992, the effective temperature of the hot component may have declined by 10-20, but this decline is comparable to the measurement errors. Optical observations of H beta and He I emission show a clear illumination effect, where high-energy photons from the hot component ionize the outer atmosphere of the red giant. Simple illumination models generally account for the magnitude of the optical and ultraviolet emission-line fluxes. High-ionization emission lines-Ne V, Mg V, and Fe VII-suggest mechanical heating in the outer portions of the photoionized red giant wind. This emission probably originates in a low-density region similar to 30-300 AU from the central binary. References: 65
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