  I briefly describe a few important scientific issues that could be addressed
effectively via the combination of data from JDEM and X-ray missions. The
topics covered are largely focused on active galactic nuclei (AGN) and include
(1) the selection of AGN via X-ray emission and optical variability, (2)
nuclear outbursts in galaxies due to transient fueling of their supermassive
black holes, (3) moderate-luminosity AGN at high redshift (z > 4) found via
application of "dropout" techniques to X-ray sources, and (4) the host-galaxy
morphologies of X-ray selected AGN. I also describe the substantial challenges
to obtaining wide-field X-ray data with sufficient sensitivity to complement
JDEM properly.
