Far-Infrared Source Counts and the Diffuse Infrared Background

The cosmic far-infrared background is now well measured from 140 micron to 1 mm. Uncertainties remain at 100 micron (and even more at 60 micron). These are dominated by limitations of the zodiacal model. The nature of sources dominating the background near its maximum are beginning to be studied through deep surveys carried out with ISOPHOT. These surveys show very steep number counts and fluctuations of the background due to unresolved sources.