The authors of this work (doctors, engineers and researchers) have endeavored to supply validated and easily understandable scientific information on the electromagnetic fields and their biological and health effects. After a general review of the physics of the waves and a presentation of non-ionizing radiations, the authors review the main emission sources encountered in our daily environment. They summarize simply but as accurately as possible the current knowledge on their biological effects.The safety limits recommended by international organizations are presented for the different frequency ranges. ;