High-Redshift AGNs and the Next Decade of Chandra and XMM-Newton
  We briefly review how X-ray observations of high-redshift active galactic nuclei (AGNs) at z = 4-7 have played a critical role in understanding their basic demographics as well as their physical processes; e.g., absorption by nuclear material and winds, accretion rates, and jet emission. We point out some key remaining areas of uncertainty, highlighting where further Chandra and XMM-Newton observations/analyses, combined with new multiwavelength survey data, can advance understanding over the next decade. 
W.N. Brandt and F. Vito
astro-ph.HE astro-ph.CO astro-ph.GA