Fluctuation analyses of the X-ray background

We review recent progress in the use of analyses of fluctuations in the cosmic X-ray background (XRB) to determine the source counts below the detection thresholds. Three flux domains are discussed: the range around 10^?12erg cm^?2 s^?1 where the Ginga and Einstein Observatory results remain inconsistent unless the sources at these fluxes (mainly Seyfert galaxies) are highly absorbed at low energies, the 10^?14erg cm^?2 s^?1 zone where the flattening of the source counts predicted by fluctuation analyses of Einstein Observatory images is now confirmed by Rosat, and the 10^?15erg cm^?2 s^?1 flux domain, where fluctuation analyses of Rosat images show that source counts remain subeuclidean with very little contribution to the XRB coming from these sources.