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The terrestrial environment is continuously exposed to electromagnetic radiations which set up a «background»
 electromagnetic noise. Within the Non Ionizing Radiation band (NIR), i.e. for frequencies lower than 300 GHz,
 this background can have a natural or an artificial origin. Natural origins of electromagnetic radiations are generally
 atmospheric or cosmic while artificial origins are technological applications, power transmission, communications,
 etc. This paper briefly describes the natural and man-made electromagnetic noise in the NIR band.
 Natural noise comes from a large variety of sources involving different physical phenomena and covering a wide
 range of frequencies and showing various propagation characteristics with an extremely broad range of power
 levels. Due to technological growth man-made electromagnetic noise is nowadays superimposed on natural
 noise almost everywhere on Earth. In the last decades man-made noise has increased dramatically over and
 above the natural noise in residential and business areas. This increase has led some scientists to consider possible
 negative effects of electromagnetic waves on human life and living systems in general. Accurate measurements
 of natural and man-made electromagnetic noise are necessary to understand the relative power levels in
 the different bands and their influence on life.