Suspected to produce harmful consequences on health, the effects of electromagnetic fields of power lines have been extensively studied in the last 30 years. The paper will present a review of epidemiological and experimental studies performed in different countries and by international bodies. Even if an electro-sensitivity for certain persons can not be denied, studies on plants, animals and humans could not put into evidence a clear effect of such fields, at levels of intensity to which people are submitted in the each day life. The standards written to fix limits for the fields on international level and the application of these standards to a real case will be shortly presented and discussed.