  We discuss the contribution of the blazar population to the extragalactic
background radiation across the electromagnetic (e.m.) spectrum with particular
reference to the microwave, hard-X-ray and gamma-ray bands. Our estimates are
based on a recently derived blazar radio LogN-LogS that was built by combining
several radio and multi-frequency surveys. We show that blazar emission
integrated over cosmic time gives rise to a considerable broad-band non-thermal
cosmic background that dominates the extragalactic brightness in the
high-energy part of the e.m. spectrum. We also estimate the number of blazars
that are expected to be detected by future planned or hypothetical missions
operating in the X-ray and gamma-ray energy bands.
