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In the previous two sections, we described the main properties of AGN continua for both obscured and unobscured sources, while neglecting the problem of disentangling the AGN emission from that of the host galaxy. Type I AGN are easily detected in the optical down to luminosities that are intrinsically weaker than the total host galaxy emission. In this case, high signal-to-noise and careful galaxy subtraction can detect the central AGN emission (Ho, Filippenko, & Sargent 1999). Type II AGN, however, can be extremely elusive, even when they dominate the bolometric emission of the galaxy, since most of their primary emission is thermally reradiated into the IR. Since the IR is simply a sum of blackbodies, to a good approximation all signatures of the origin of the luminosity are lost. Hence it is extremely difficult to distinguish an AGN contribution from that of star-forming regions. This problem is particularly important in the study of high luminosity sources, such as the Ultraluminous Infrared Galaxies (ULIRGs; Sanders & Mirabel 1996) and their probable high redshift analogs, the powerful submillimeter emitters detected in SCUBA surveys (e.g., Smail, Ivison, & Blain 1997; Barger et al. 1998; Hughes et al. 1998). Distinguishing AGN contributions from star formation is of great importance in determining which class of source makes up the submillimeter/IR background, and therefore in knowing the relative contributions that accretion onto supermassive black holes and star formation make to the total luminosity of the universe.