Use of microwave radiation as a source of energy has been increased in recent years. The existence of high-power microwave emitting sources, such as satellite and television communications systems, radar systems and heating devices, in both the general public and industrial environments raises the question of whether exposure to microwave radiation is detrimental to health. The use of microwave devices in home and in medicine, e.g. in clinical diagnosis and in therapy, also makes the investigation of the biological effects of acute and repetitive exposure imperative. In this work we present some characteristics of microwave radiation, and the possible effects on some systems under the conditions of different forms of microwave irradiation, on experimental animals and on the people who have been professionally or ignorantly irradiated.