  The Spitzer Space Telescope revolutionized studies of Active Galactic Nuclei
(AGNs). Its combined sensitivity and mapping speed at mid-infrared wavelengths
revealed a substantial population of highly-obscured AGNs. This population
implies a higher radiative accretion efficiency, and thus possibly a higher
spin for black holes than indicated by surveys in the optical and X-ray. The
unique mid-infrared spectrographic capability of Spitzer gave important
insights into the distribution and nature of the dust surrounding AGNs,
enabling the separation of AGN and starburst components, the detection of
silicate features in emission from hot dust, and the identification of shocked
gas associated with AGN activity. The sensitivity of Spitzer allowed almost
complete identification of the host galaxies of samples of AGNs selected in the
X-ray and radio. As we look forward to the James Webb Space Telescope, the
lessons learned from Spitzer studies will inform observational programs with
new and upcoming infrared facilities.
