Some of the high-energy photons emitted around AGN will be absorbed by surrounding dust grains. The reprocessed thermal emission by dust grains then glows in the mid-infrared regime (peaking around 10-20 microns). Dust near the AGN can reach up to its sublimation temperature. It is therefore much hotter than the bulk of dust grains heated by star formation and so its mid-IR emission can fill the through between the stellar bump (at ~1 micron) and the cooler dust emitting in the far-IR (at >40 micron). The details are more complex than this simple picture, but there are broadly two ways to select AGNs in the infrared regime: one that relies on this hot dust component and its influence on the IR colors; and another that instead relies on emission lines tracing the ionized gas and the excitation properties (e.g., fine structure lines).