The peak region of the extragalactic background radiation
  The Cosmic X-ray background carries the information of cosmic accretion onto
super-massive black holes. The intensity at its peak can be used to constrain
the integrated space density of highly obscured AGNs. Determining the shape and
intensity of the Cosmic X-ray background radiation represents, however, a first
step towards the understanding of the population of Comptonthick AGNs. The
study of AGNs in the local and more distant Universe allows to understand the
whole picture. In this talk, I will review the current understanding of
generation of the Cosmic X-ray background at its peak. I will focus on the
recent measurements of the Cosmic X-ray background and I will discuss the
recent advancements in the understanding of AGNs in both the local and more
distant Universe. Finally, I will also discuss open issues and future
prospects.
